"Who is to bell the cat?"
Who will risk his own life to save his neighbour's? Any-one who encounters great personal hazard for the sake of others is said to "bell the cat" The allusion is to the fable of the cunning old mouse (given in Piers Plowman and elsewhere) who suggested that they should hang a bell on the cat's neck to give notice to all mice of her approach. "Excellent", said a wise young mouse, "but who is to undertake the job?"

Quoted from the Wordsworth Dictionary of Phrase and Fable - lots of other "cat" references too!