A painful white, or sometimes red bump in your mouth. You might get them on the inside of your lips, the inside of your cheeks, or anywhere in your gums. They're normally caused by putting something dirty in your mouth, such as keys, or simply putting money in your mouth (nickles, quaters, dimes etc.) or even not washing your fruits! These things usally last for 1 or 2 weeks. It heals better if you don't put any treatment on it. But try advil to reduce the pain.
Oh damn, i shouldnt've eaten that un-washed apple! I think i got a canker.