I've only come across it as an extreme fearresponse - when the rabbit is dying or thinks it's a bout to. A sort oflast ditch effort to make a 'preditor' pause. It doesn't surprise methat it upset bunnies hearing it. Rabbits work as a group to protectthemselves, signals like the scream, thumping and the white flash ofthe underside of a rabbits tail as it bolts are all signals to the restof the group there is danger. Your thumbing bunny was passing thewarning on to you that you needed to take cover asap.
Rabbits can make weird vocal noises like buzzes, squeaks and humms butI haven't heard of a scream being anything other than fear. Interestingto hear that other people have come across it.
Tam