Better to avoid
No — bread and rabbit digestion are a bad match. Starchy foods ferment in the cecum, disrupt gut flora and can trigger GI stasis, the most feared rabbit emergency.
Rabbits run on fibre. Their cecum is a fermentation vat tuned for grass and hay; flood it with starch and sugar from bread, crackers or cereal and the wrong bacteria bloom, producing gas and toxins. This can escalate from soft stools to full GI stasis — when the gut stops moving — which kills rabbits within days if untreated. Old advice about giving rabbits bread crusts “for their teeth” is exactly wrong: teeth need hay abrasion, not starch.
None. A stolen crumb isn’t a crisis, but bread should never be offered. If your rabbit ate a meaningful amount of bread (or any starchy food) and then slows down eating or pooping, treat it as an emergency and call a rabbit-savvy vet immediately.
For chewing enrichment use hay cubes, apple-tree twigs (unsprayed) or willow toys — teeth and gut both win.
This article is general information, not veterinary advice. If your pet has eaten something potentially harmful or shows symptoms, contact your vet or an emergency clinic immediately. Full disclaimer.