My inevitable response is "blue". In France, of course, I'd say "bleu". In France this is often met with a quizzical look and a raised eyebrow followed by "mais, vous etes Anglais". The English are supposed to always cook everything until it's dead, dead, dead.
I don't know the French for "kill the cow, wipe its bum, put it on the plate", but if I did that's what my response would be. I've been known to utter this phrase in England to waiting staff who don't seem to know what "blue" means.
Here's my fillet from the Italian place we ate in in Truro as an example of how to cook a steak properly blue, sealed on the outside and warm right through: