Mouse is tremendously curious. He has to investigate everything around him. And Mouse’s friends don’t escape his inquisitive nature. Mouse wears a nappy, and naturally he is curious about theirs … So one by one, Mouse asks his friends Rabbit, Doggy, Horse and others, ‘What’s in your nappy? Then, of course, they ask Mouse the same question – but they’re in for a surprise, because in Mouse’s nappy is … nothing! He’s learnt how to use a potty, and on the final spread all his friends try it, too (on their own potty).