What happens if a rabbit eats iceberg lettuce?

yes

What is an Easter Bunny? The Easter Bunny is not a real animal, so it doesn't eat anything at all. Bunnies that people get as gifts for easter eat the exact same things as all other pet bunnies: lots and lots of hay, some leafy greens, and some pellets.

Dark lettuces (like red leaf, green leaf, escarole, endive, Romaine, Boston, etc.) are good for rabbits in moderation: they can have some in their daily "salad" often, but not every day. Too much lettuce can lead to diarrhoea and illness.

Light lettuces (like Romaine hearts, iceberg, etc.) are not healthy for rabbits: they have no nutritional value, and they can more easily lead to diarrhoea than the dark varieties. They should be avoided entirely: don't feed any to your bunny.

See the related questions below for more info and links.