The reason that snakes, scorpions or other venomous creatures don’t poison themselves is because it’s kept in a very special compartment in the body, specifically designed not to let the venom out and not to be sensitive to the effect of the venom.  In a snake’s poison glands, there are specialised cells which have genes activated which tell them how to make the cocktail of proteins (snake venom is a protein) which makes up the venom.  The venom is then squirted out into a special system of ducts, lined with cells designed not to be sensitive to the venom.  The venom is produced, it trickles down these ducts and into a special bag which holds it and keeps it safely away from the rest of the snake’s body until it’s needed.

A snake’s teeth are hollow and, in the case of the cobra, curved.  This means that when the snake wants to bite something, it can lock on to its prey and hook its teeth in.  Muscles around the venom bag then contract, squirting the venom out through the hollow teeth and inside the tissue of the victim.

Normal tissue lacks the specialist defences found in the venom producing glands of the snake.

This is very similar to the human stomach.  We make digestive juices in the stomach including acid and enzymes which could break down our body’s tissues.  They are stopped from doing this by the stomach’s special lining, which protects it from the effects of the digestive juices.

If you were to inject cobra venom into the normal tissue of a cobra, it would have the same effect at it would on you!

The sun itself is made of gas, mostly hydrogen and helium, and so does not have a solid surface like you would find on Earth or Mars.  However, if you look at a photo of the sun you can see it has a definite edge to it. This is not because the gas stops at this point, it actually carries on diffusely for thousands of kilometres.  The Sun is hotter in the centre and cooler towards the outside, and there is a point where the hot gas becomes cool enough to become transparent, so this point is what we see as the surface of the Sun.

The surface of the Sun is about 5000 degrees Celsius, but inside its millions of degrees.  Nuclear fusion reactions occur inside the Sun, much like nuclear bombs going off all the time.

There is also material streaming off the surface of the Sun all the time, which forms the “Solar Wind”.

In hard water areas, the water contains quite a lot of calcium in the form of ‘temporary hardness’ – calcium hydrogen carbonate Ca(HCO₃)₂.  When this is heated, the temporary hardness breaks down into calcium carbonate, which is chalk, and water. 

These calcium salts can bind to tannins in the tea and form an insoluble precipitate - a scum.  These particles float to the top of the tea, and stick to the side of the cup.  Tannins contain some of the colour of the tea, and so this ring of particles will be dark, and stain your cup!

The reason it ripens is because bananas happen to produce a huge amount of the ripening chemical that fruit uses, Ethylene.  It’s the same stuff that can be processed to create polyethylene – plastic.  Bananas secrete loads of ethylene, and so it will spread to any other fruit in the fruit bowl.  All fruit use ethylene as a signal to ripen, so this is a natural way to encourage fruit to ripen.

If you traumatise a plant, such as by pulling leaves off, it will release a burst of ethylene as a growth signal to the rest of the plant.

Leeches are a member of the worm family, and do not have to live in water, as long as they don’t risk drying out.  It’s unlikely that they will harm you; in fact medically speaking leeches have been used for centuries.

The saliva of leeches contains a natural anti-coagulant called hirudin.  This stops blood from clotting.  If a surgeon needs to reattach a body part, it’s relatively easy to attach the arteries that supply blood, but much harder to attach all the tiny veins which allow blood to get back out.  When lots of blood goes in and can’t get out this creates blood clots which can cause tissue to die.  If you attach leeches, they suck out some of the blood, establishing blood flow and avoiding clots.

Flames are simply soot particles made when a wick (in the example of a candle) burns.  Because these soot particles are so hot, travel upwards and glow, just as a red hot poker might glow.  They glow a yellow colour and so create a flame.