Rabbit is the mildest thing in the shop. Ears with the fur still on, skin strips, and the small sausages and nibbles that get used for training.
It is usually the first protein tried on a dog that reacts to beef or chicken, because almost no dog in this country has eaten it before. That is the whole point of a novel protein: a body cannot be sensitised to something it has never met.
Nothing here lasts long. An ear is gone in a few minutes for most dogs and the skin strips faster than that. This is a treat, not a way to occupy an afternoon.
The fur is deliberate. Roughage moves through the gut and takes what it finds with it, which is why hairy ears have a long reputation as a natural wormer. High in protein, low in fat.
Smell and mess: about as little of either as a natural chew gets. Dry rather than greasy, and nothing that carries to the next room.
For working out which protein to try first, read hypoallergenic dog chews.