Can rabbits eat grass?
Yes, it helps their digestive system.
Pet rabbits can eat grass as a treat but more importantly they should eat lots and lots of grass hay (dried grass available in pet stores and feed stores). Rabbits need hay to help keep their teeth nice and short (their teeth grow their entire lives). Wild rabbits eat a lot of woody materials like branches and twigs, and they have to chew through thick fibrous materials like roots when they make their burrows, so their teeth stay worn down naturally; but pet rabbits don't have these things, which is why you need to give them hay, not just fresh grass.
There are risks involved with giving your rabbit fresh grass. For instance, there could be pesticides, car exhaust, or other toxins on the grass. There could also be parasites on the grass, which can be left behind by other animals when they defecate on the grass. (Even if the feces is removed or washed away, the parasites could remain).