QI, Series Four [D]

Roger McGough:
[reciting a poem] A crab, I'm told, will not bite, Or poison you just for spite; Won't lie in wait beneath a stone, Until one morning out alone, You poke a finger like a fool Into an innocent-looking pool; Won't grab your hand And drag you off across the sand Down into the bottom of the sea To eat you dressed for Sunday tea. The crab, I'm told, is a bundle of fun. With claws like that? Pull the other one!