I think the world of animal behaviour, and of human behaviour, for that matter, is full of situations in which signals are cost-free because there's no conflict of interest between signaller and receiver. I'd like to give you an example, this is going back to my fruit fly days. In Drosophila subobscura, females do not mate twice. If they've been mated, they will not mate again, and there's no way a male can force a copulation on them or, he can mate... he can court till the cows come home, she won't mate. If you put a mated female with a male, the male approaches her and starts doing his stuff, and she turns... bends her abdomen towards him and extrudes the ovipositor, and that is a signal saying, 'Look, mate, I'm mated.' And he stops at once. Now, I think this is a cost-free signal. It doesn't pay the male to ignore it, because, you know, he's not getting anywhere. It costs the female practically nothing to extrude her ovipositor. She gains by it because she's not continuously harassed when she's trying to feed, and so on, he's not getting in her way. This is just an example of a context in which I think, if there's no conflict of interest between male and female or between signaller and receiver, then signals can be cost-free.