I just remembered one. But I'll post more than one. Also these are probably very easy.

A group of friends were telling war stories about their grandfathers. In particular, one of them had a very interesting story. "My grandfather, after losing an arm in the war, was to recieve a medal. When he was told he would get an even grander medal if he had lost both arms, he took a knife and cut off the other arm!" None of the friends believed this story at all. Why?

And another...

After discovering a new planet, a space explorer decided to count the population of Octopleans on the planet. She counted 379 male Octopleans, 493 female Octopleans, and 125 that had the features of both male and female Octopleans. Right now, how many aliens are there on this new planet?