I saw a mouse hide in that hole.
I saw a mouse hiding in that hole.
Which one is better?
They are both grammatically sound, but they have slightly different meanings. If you saw the mouse hide, then you actually saw it go to hide; you saw it entering the hole. If you saw it hiding, you might just have peeked in and seen that it was already there. Equinox◑ 13:21, 18 March 2009 (UTC)