Could it be a bug bite? Has your bunny been outside? I would not take the rabbit to the vet and just put Vetericyn on it for a day or two. Vetericyn is used for any cuts, and just needs to be for rabbits. Mineral Oil is used for ear mites though I personally don't think ear mites are the problem. DO NOT put the Vetericyn in their ear. You can rub it on with a q-tip.