We don’t use oxygen for this because oxygen is very good at oxidising things, and will make them go off.  This will make your drink taste nasty.  Carbon dioxide is basically a neutral chemical; it doesn’t react with much, so it shouldn’t make your drink taste bad.

Carbon dioxide is also acidic and when it's dissolved it makes carbonic acid, which gives a nice, lemony, sparkly taste in your mouth.

Even when it looks like a drink has gone flat, there’s still a lot of carbon dioxide dissolved in it.  Sprinkling salt or sugar in the drink will create lots of 'nucleation' sites on which bubbles can form, so some fizz will come back.

It’s true that nylon football shirts will cause a spark, as will nylon underwear!  
The theory with mobile phones is that they emitt microwaves, which can interact with metal to induce a current and then possibly create a spark.  We’re not sure this has ever been demonstrated with mobile phones, but we’ve all seen sparks from nylon clothes.

As to the likelyhood of a phone causing a fire compared to a nylon shirt causing a fire, we dont know!

So maybe we should ban nylon clothes at petrol stations!

Contrast is a substance you inject (or administer) into people, which is usually something like Barium or Iodine (hopefully you wouldn’t inject Barium – it’s not very nice) these have big nuclei which scatter x-rays.  They circulate in the blood stream and if you have a cancer or something, the blood vessels which supply cancer are leakier than blood vessels supplying healthy tissue, so you tend to get a build up of contrast agent in the abnormal area.

When the scanner comes on, the x-rays go right through normal, healthy tissue, but where the contrast is they get scattered and soaked up.  This means they don’t get through, and this makes the tumour or abnormality glow up which lets you pinpoint areas of abnormality using the contrast agent.

Simply put, it makes areas of damage easier to see.

This is called a Hypnic Jerk.  When you go to sleep at night your brain paralyses your body to stop you acting out all your dreams.  It would be dangerous to act out everything that happens in your dreams, especially if you were running or fighting, not just for whoever shares your bed, but also for yourself.  It’s thought that this ‘sleep paralysis’ evolved when we slept in trees, as acting out your dreams whilst sleeping high up in the branches would be even more dangerous than doing do while tucked up in bed!

As this system kicks in, you can sometimes have these hypnic jerks, where all the muscles contract suddenly and violently. For some reason, these are often associated with dreams of falling.