I've reinstated the game of "surprise turd". The rules are quite easy; you simply wait until They are out and then leave a little surprise where they won't expect it.

The best fun to be had is where one of Them finds it and not the other. If He finds it he moans to Mummy and doesn't get believed. If Mummy finds it she throws it away quickly without saying anything to him and then tells me how clever I am.

May have to up the stakes at some point. Perhaps another dead sparrow...