This is a really good question and in fact they do.  Bees do have segmented legs, consisting of parts called a coax, a trochanter, a femur, a tibia and a tarsus.  The jointw between which must be considered to be 'knees'.

There’s been some discussion on the Naked Scientists’ forum about this and Turnipsock suggests that perhaps the expression "The Bee's Knees" comes from the fact that they store pollen in these hairy baskets on their knees.  They have hairs on their knees which are used to collect a big build-up of pollen.  So, this could look like something very big and spectacular, hence the expression.

Well, let's start off with something a bit smaller.  When the impact which we think wiped out the dinosaurs hit; a 10-15km asteroid was thought to have hit somewhere in Mexico in Chicxulub.  Just the 10-15km asteroid hitting the Earth released about the same energy as 100,000,000,000,000 tonnes of dynamite exploding (or TNT).  Just to compare to that, the biggest nuclear bomb we’ve ever built was the equivalent of 50,000,000 tonnes of TNT.

If you scale that up to something the size of a planet so several thousand kilometres across the amount of energy released is going to be absolutely immense.  We think that Earth was originally hit, or what we call proto-Earth - Thea, was hit by an object the size of Mars about 4.5 billion years ago.  When this hit the Earth it collided and released absolutely immense amount of energy. It completely melted everything in the Earth. The core of the other planet went in and ended up coalescing with the core of the Earth and then there was a load of stuff thrown out: an immense amount of the lighter rocks on the surface. These coalesced into a ring and then probably coalesced into the moon. So the moon is made of much lighter rocks than the Earth. The Earth is denser than it ought to be because it’s just the two cores.

If you have a planetary collision it’s messy but it can give rise to whole new worlds!

The first thing to note is that grey hairs are not grey.  They’re actually white because hair colour is determined by pigment that is made by hair follicle cells.  There comes a time in everyone’s life where basically the pigment stops being produced.  You start producing hairs that have no pigment so they’re white. This mixed with your hair colour gives the grey effect.  Rather than hairs starting coloured and going white, although that is possible, you tend to get hairs that start off being white.

Another question is, does people’s hair really go grey overnight?

Kat:  I have looked at it a bit and there seems to be a bit of an argument in it. The only way I can see it’s possible is if someone has very short hair. They go grey due to some stress event. Maybe their hair’s falling out.  It might look like over a very short period of time if you have very short hair that you’re going grey overnight.

Chris: I’ve seen patients who have a hair which they’ve showed me themselves and say, “This is interesting doc, look at this.” It’s white at the base and then brown halfway along because it’s literally run out of melanin to add to the hair and it’s changed colour.

This is a fantastic question!  You can achieve the same effect, not necessarily with an up thrust of wind, but also by crunching your cereal.  If you were to go along in a car and eat some cereal at the same time you would see the same effect.  Also, if you’ve got an LED clock radio at home you can achieve the same optical illusion looking at the display - the numbers appear to jump or flicker on and off as you chew.

What’s happening is you’re creating your own in-body stroboscopic effect.  The vibrations when you’re eating are being transmitted to your eyeballs and they’re making your eyeballs move very slightly.  This rapid eyeball movement is capturing the movement just the right way of those nuts going round the wheel or the flickering of LED clock lights.  So this creates the appearance of jumping or freezing or switching off for a fraction of a second.  It’s literally your eyes moving together in unison as a result of crunching or burping or making a movement which jolts your eyeballs a little bit in your head.

Yes.  In theory you could do that.  Blood is actually full of protein and it’s full of iron, which you need in your diet.  Don't forget that black pudding is just congealed blood that you fry.  Blood also contains water which you need and there are some salts in there,  so you can get protein, salt and iron from drinking blood.

There will be other things that you can’t get from blood like water-soluble vitamins which are not present in large amounts.  There will also be some fat-soluble vitamins which don't appear in large amounts in blood.

You can probably make a reasonable meal out of blood but it wouldn’t make up for all of your dietary requirements and so you might want to eat some freeze dried body pellets to supplement your intake.  That’s no different, really, from eating a microwave meal which is effectively just a dried out bit of body.  It may not be human, it’s just animal instead.

We’ve gone to the forum for this one.  Basically it’s visible because when it’s in the sky it’s just another object being lit by the sun.  So when it’s in the right place we can see it.

The moon is orbiting the Earth once every 28ish days.  You can’t see it during the day if it’s right between us and the sun because the back of it, which isn’t lit up by the sun, is pointed towards us.  If the moon is around 45 degrees off the sun or even 90 degrees off the sun then half of it will be lit up really quite brightly. Then the surface of the moon is about as bright as the surface of the Earth is.

There’s no reason why you shouldn’t be able to see it!  As long as the moon’s at 45 degrees the sunward side of the Earth and it’s lit reasonably you’ll be able to see it.

The process is very likely to be the same as any other hair colour.  All you’re doing is losing from the hair the ability to add some colour. The colour is accounted for by different forms of melanin: the same hormone, the same chemical in the skin that makes you go brown.  You just lose the ability to add that to the hair so you see the natural colour of the hair: the keratin and that’s the stuff which is white.

This is a semantics issue.  A meteor is a lump of rock on collision course with something - they’re whizzing towards them.  When they hit the ground they become a meteorite - a congealed lump of rock which has melted on the way through and landed on the ground. So a meteorite is something which has made it to a planet’s surface.  An asteroid is a huge chunk of debris left in space which is effectively a failed planet that never managed to form.

The same amount of energy will throw more material around.  However, because the moon has less gravity, the same size meteor hitting the moon will have less energy than it would if it hit the Earth.  For a collision with the same amount of energy you’ll get a bigger crater on the moon.  The big effect on the moon is they’re not getting eroded all the time by wind and weather.

Well, actually you could sit on an electricity wire and not get electrocuted as long as you didn’t touch anything else.  The birds aren’t doing anything special.  The reason they’re able to sit there is because they’re not earthing or producing a route for the electricity to get from the wire down to the ground.  If you were to hang on to the wire and touch the pylon that’s holding the wire then you’d have a problem.  The wires are at a very high voltage, the pylon’s at a very low voltage and you provide a very convenient circuit down to earth for the electricity. The birds that are sitting on the wire there’s no difference in potential between one leg and the other. Both legs are sitting on the wire so there’s no reason for the electricity to want to flow through them.

The answer is definitely no.  In hospital they use things called vacutainers which is a vacuum in a tube.  You put a needle into a patient’s vein, put the tube onto the needle and this exposes the inside of the vein to the vacuum and draws the blood into the tube. Momentarily the blood is exposed to a vacuum and the blood comes out very red.  There’s still too much oxygen in venous blood to make sure it stays a red colour.

So why do veins look blue?

This is because when you have a bit of the tissue which doesn’t have enough bloodflow going through it tissue will remove more oxygen from the blood.  It does mean haemoglobin can get to be a blue colour.  Normally that doesn’t happen but if you have an area of the body that doesn’t have enough bloodflow through it then the tissue gets oxygen hungry and removes enough oxygen to make it go blue.  Veins look blue as an optical illusion.  They’re not really blue and if you cut through the skin you’ll see they’re a whitish pink colour.

When air is hot it expands and light will go through hot air slightly faster than cold air. When light changes its speed at an angle it will bend like when it goes into glass or something.  You get lots of turbulence with air moving up which light will go through faster. So you get light bending in all sorts of directions which change as the air moves and you get this turbulence effect.

The same effect makes stars twinkle, as you get turbulence up in the atmosphere which bends the light coming from stars which makes them twinkle on and off.  Sometimes they come towards you, sometimes they go the other way.