Thank you very much! I got this rabbit a few days ago to make her a girlfriend of my other rabbit. The other rabbit always pursues her so pressure could be a reason.It's the third eyelid. Usually it shouldn't be protruding like that. It can happen when a rabbit is stressed, but should return to normal when the rabbit calms down. If it's not going back to normal with your rabbit, it's possible it is health related. One possibility is a heart issue, so you will want to make sure your vet checks your rabbits heart function to make sure that isn't the cause.