You can choose any song that you all know. The point of this game is to sing this song not in a simple way, but in a funny way. For example you can offer to sing it as a chicken, as a dog, Winnie-the-Pooh, etc.
The first player tells the second one, which animal or character he should imitate.
After the second players sings, he tells what character should be imitated by the third player.
And so on.