Really useless trick, but can be fun to watch. 

What happens is that you can make a firewarrior do the tree chopping animation, but it will not actually cut the tree - so yeah, preety useless trick.

All you have to do is select a brave, hold Ctl, click on the firewarrior hut, then click on a tree. This will make the brave to get trained into a firewarrior, who will later try to cut the tree, without sucess. If you do this with a spy, he will actually cut one piece of the tree!