A hair is made of keratin which is the same protein that makes up finger nails which is white. On your head you have a group of cells specialised for making keratin, and near them you other cells called melanocytes which make the dark browney black pigment called melanin (its job is to absorb ultra violet light and protect the skin) a lot of these keratin making cells are squashed flat and painted with pigment, squirted through a nozzle called a folicle and form a hair. Sometimes for reasons that are not well understood, these melanocytes seem to burn out leaving the hair its natural white colour. Grey hair is actually a mixture between normal dark hairs and white hairs, which if you are standing a way away look grey.

It is only the female mosquito that drinks your blood, they need the protein to make all their eggs. Male mosquitoes and females the rest of the time just eat nectar. It is very hard to eradicate mosquitoes, because they are not very fussy about what kind of animal they drink from. However the Poison Arrow frog can fight back. It is extremely poisonous, and when the mosquitoes drink its blood, they rapidly die.

You may have heard of surface tension this is due to water molecules pulling together and trying to minimise the number of them on the surface and not surrounded by other water molecules, it can hold up pond skaters and float pins etc. Now the water in the soap film is trying to minimise it's area too, and as there is a fixed amount of air trapped within the bubble and the shape with the least surface area for its volume is a sphere, bubbles are spherical.

The way your voice works is that your vocal chords vibrate and make a series of different frequencies. Your throat and mouth act as a resonant cavity. This is a bit like a tray of water, you can vibrate it at lots of different frequencies and not much will happen, but if you vibrate it at the same speed as a wave will travel up and down it, the wave will get stronger and stronger. Similarly if you vibrate your throat at the right speed the vibration will get stronger and stronger so you throat will amplify some of the frequencies your vocal chords are making (by changing the shape of your mouth you can alter which ones are strengthened which is how you make different vowel sounds). Sound travels faster in helium so the vibrations will get from your vocal chords to your mouth quicker so your throat will resonate at a higher frequency and hence a higher pitch.

WARNING - There is no oxygen in a helium balloon and your body has no way of detecting that it is short on oxygen so you will feel fine until you fall unconconcious. So it is recommended you don't try and replicate this. If you must have a go, don't take deep breaths of helium or more than one breath of helium every few minutes.