I was going to mention crouch jumps - and obviously you know those, as I expected. Really it's just the same thing going on; a knees-up action, followed by falling. At least, that's what I'm assuming (I could do with seeing an actual crouch animation).

If that's right, in a sense we've got a 'knees up' button, not a crouch button. But of course, in normal circumstances MC quickly settles on the ground after the knees-up animation, and then you've got a 'crouch', in the normal sense of the word.