Standing on your hind legs - which is the behaviour under discussion - is costly to rabbits - since it increases the chance of being observed by predators - so they can't do it all the time.
However, that is not really the point. The signal is not: "look how fast I can run" - it is "look how much of a head my family and I have - given that I can see you now".
Standing on your hind legs - which is the behaviour under discussion - is costly to rabbits - since it increases the chance of being observed by predators - so they can't do it all the time.
Not only that, you can only look in one direction at a time. You do need to know where the fox is. The rabbit only loses a couple of hundred milliseconds if the fox decides to make a dash for it anyway.
Sweet, there's another Bloggingheads episode with Eliezer.
Bloggingheads: Robert Wright and Eliezer Yudkowsky: Science Saturday: Purposes and Futures