I agree that the pink spot is a sensory area. They've had that area since the first movie, but it wasn't so pronounced. All the facehuggers in previous movies had their hosts waiting just outside the egg, but in avp-r, they've been locked in stasis for who knows how long, that the original prey has already passed on and once it awakens from stasis, it will probably have developed a new way to find prey, because the last thing it remembers was the host being there, but then he wasn't. Maybe a long range heat sensor?