Aside from being indoor free roam and litter trained rabbits, they are also dedicated alarm systems.
Now, rabbits don’t make any vocal noises, aside from the odd grunt or squeak. But nugget and snuffles will bound into the room you’re in and thump their little back legs down on the carpet/couch/my lap (ouch) if they hear anyone at the front door. Or if they smell a cat. Or if you have popcorn and they want it.
