I did wonder if the plant might be horehound... which is why I asked about the smell. I doubt it will be of much use to the rabbits, but it is excellent medicine when you have a cough or cold. Dry some to use for a medicinal tea (it is bitter, so will need sweetening) or make horehound candy to suck for a sore throat. A time-honoured remedy and there are plenty of recipes on the Internet.