This is usually the "Sole game" we play on barefeet but I adapted it to play on Rachel Adams' super ticklish bare belly. Rachel has to keep her eyes closed while I trace a letter or a number on her bare belly with the feather or my fingers. If she guesses it wrong, she gets tickled harder on her belly and sides. I make the game unwinnable of course and Rachel loses according to me. So she gets tickled all over her belly, sides, ribs and armpits at the end for losing the game :)