Tongue Osmosis

Ever bite your tongue or your cheek? Here is an interesting science experiment you can do to make yourself feel better next time it happens.
Take a small drink of pure water — bottled reverse osmosis water works better than tap water. Notice how the owie on your tongue hurts more? Now take a drink of a dilute cool-aid or soda, or milk, or even a little salt water. Your tongue feels better!
The pure water is absorbed by the cells of your tongue inside the cut where you bit yourself. Those cells swell up, possibly even bursting. The swelling and dying of cells triggers a pain response.
The other solutions contain dissolved molecules of sugar or salt. Those solutions have a similar osmotic potential as your cells, so water doesn’t move into cells. Thus those things don’t hurt to drink.
Canker sores are another thing altogether — and drinking too much soda (even though it is osmotically gentle) can cause canker sores, in my opinion. But actually, canker sores aren’t well understood biologically.