The human body is a strange and mysterious place filled with gross guts and gurgling magic potions. There are all sorts of confusing or nonsensical processes our own bodies perform that we just shrugged off and accepted way back in childhood. Fortunately, good ol' science is finally here to explain things like ...
Your eyes are immensely intricate machines built through millions of years of evolution, so it's only reasonable that they should have developed a few glitches along the way. For instance, the dots or squiggly lines that are sometimes visible off to the sides of your visual field. They float around and then dart out of sight immediately if you try to get a good look at the bastards.
These damn things.
And then you have the bright spots that appear in front of your eyes ("seeing stars") when your body suddenly strains really hard. Maybe you sneezed, or pulled an intense, full-body Valsalva maneuver trying to squeeze out a dissident turd, or just rubbed your eyeball.
Both phenomena are completely normal, yet the explanations are weirder than you think.
It Happens Because ...
First of all, "eye floaters" are not a) just lint and shit that fell into your eye or b) unusually upstart sperm that got really really lost.
Your eyes are mostly made up of a jelly called vitreous fluid, and this gel undergoes many changes as you age. As it slowly shrinks, it loses its smoothness and starts to look stringy. The vitreous can also become more liquid, and this allows for tiny fibers in your eye to come together and form (relatively) large clumps. These get big enough to become visible and freak us out, but they eventually sink down and settle at the bottom of your eyes where you can't see them. So technically, they're your little buddies for life.
Everyone you love will die, leaving ocular degeneration your only friend.
As for the bright dots that flash and move in front of your eyes, they're called phosphenes, and they're caused when cells in your retina are messed with (by rubbing your eyes or having a large person slap you in the dark), causing them to misfire. Strangely, scientists have found that they can also stimulate phosphenes by running electricity across the visual cortex part of your brain. Try it on a friend!
But wait, it gets weirder: Have you ever gone out and stared up at a clear blue sky, only to see faint white dots dancing around the edge of your vision? Most people can see it if they really look, and it's worth it because you are seeing the goddamned white blood cells shooting through the blood vessels in your fucking eyeball. The blue light causes the vessels and other cells to be invisible to your eye, so you wind up seeing the white blood cells zipping around like tiny ghosts, just chasing diseases and shit. Maybe there's a tiny ship full of scientists in there.
Anyone who has enjoyed frozen treats ranging from ice cream to Slurpees has had, at least once in their life, a brain freeze. The name sums it up pretty well -- you're halfway through a tasty dessert when suddenly your head hurts like Ben and Jerry simultaneously drop-kicked your face in some twisted Mortal Kombat finisher. But why would it happen? It's not like a mouthful of frozen treats can actually lower the temperature of your brain or anything (if it could, a single trip to Dairy Queen would kill your ass).
Or preserve you till the year 3000.
It Happens Because ...
Researchers at Harvard, the University of Ireland, and the U.S. Department of Veterans' Affairs teamed up to figure out why the hell such a great thing can be so unpleasant (we guess it's marginally better than spending your tax dollars on another bank bailout). They came to realize that they could trigger the headaches just by placing an ice cube in the subject's mouth and pushing it to the top of the palate, which messes with the brain's thermostat.
The brain wants to keep a constant temperature, so when you're stuffing your head with ice cream, your palate gets chilled and your brain freaks out, thinking you're trapped somewhere near the peak of Mount Everest ("Holy shit, it's so cold here that the inside of his mouth is freezing!"). It opens up arteries to pump more blood to the area to warm it up, but instead of making you super smart, the increased blood pressure just causes an "ice cream headache."
Eating fire's similar; your brain assumes you're in Phoenix.
People usually respond to these shooting pains by pressing their hands to their head, as if manually warming the skull will fix it (which, as you can guess, does nothing). No, the only known way of getting rid of the brain freeze is to warm up the top palate and constrict those arteries back to normal size. Sometimes pressing your tongue against the top of your mouth can help. Or you can shove a Hot Pocket in there, whatever.
If you've never tried it, go do it now. Brush your teeth (with toothpaste) and then run to the fridge and take a drink of orange juice. Holy shit! Your sweet, sweet juice has turned into some kind of horrible chemical-tasting cleaning solution. A witch has cursed your refrigerator and/or beverages!
"Stabbing didn't help, now I just taste blood!"
It Happens Because ...
Actually, this bizarre reaction was, for some of us, our first childhood introduction to chemistry. The weird horriblization that occurs with orange juice and lots of other foods after brushing is due to a chemical called sodium lauryl sulfate. The white coats making your hygiene products know just how much you like it when your cleaning products foam up, so they have to add totally useless enfoameners (may not be the actual name). The aforementioned SLS is one such animal, and gives you that great frothy mouth-feel you need to make it seem like your toothpaste is doing something.
If you're rabidly foaming, it has to be working.
But one side effect of SLS is that it wreaks havoc on your tongue's taste receptors -- it numbs the little guys in your mouth that detect sweetness and erodes the fatty shield that blunts the taste of bitterness. For a while, anyway.
So your mouth is getting double-teamed into a gustatory lethargy, which has the effect of significantly changing the way certain foods or drinks taste to you. Obviously it's more noticeable on substances that are normally super sweet yet acidic (other foods may just taste a little lifeless). If this bothers you, there are actually toothpaste brands that don't have SLS or its sweet foaming action. But if you live with someone else, you've got about one day before they start screaming from the bathroom that your toothpaste is broken.