I saw this puzzle a while back in a children's puzzle book, but I'll try to make it as accurate as possible.
There is a small army of three ants walking down a very narrow road, so there is only room for them to walk single-file. They come across another small army heading the opposite direction. Neither army wants to fight (ants are peaceful, I think), but it seems as if they have no options. Fortunately, one clever ant spots a small clearing in the trees, that only one ant can fit into at a time. Can the armies pass each other without having to fight? If so, how do they do this?
I have made a very bad illustration of this so it will hopefully be easier to understand, but if you need clarification I can provide it. Only one ant can fit into the hole at a time, and the road is long enough for both armies to fit on one side of the hole. This is not a lateral-thinking puzzle, so don't post any answers like "These ants aren't peaceful."
Edit: I actually included the picture this time.