Hiding In A Tree

A Pole, English, and French guy are running away from the German soldiers when they come up to a forest and they decide to hide by each climbing a tree. When the Germans arrive, they go to the first tree where the English guy is, and shout:

- We know you're up there; come down.

The English guy, thinking fast, says:

- Twit, twit, twit...

The Germans, thinking that it's a bird, move on to the next tree where the French guy is and once again shout:

- We know you're up there; come down.

The French guy, thinking fast, says:

- Woo, woo, woo...

The Germans, thinking that it's an owl, move on to the next tree where the Polish guy is and once again shout:

- We know you're up there; come down.

The Polish guy thinks for a while and then says:

- Moo, moo, moo...