Thumping can mean a few things.
1) Thumping to warn of danger: Rabbit senses something dangerous and is thumping to inform you; will typically flee somewhere safe at the same time.
2) Thumping in excitement/impatience: Typically when you have food/treats, or are letting the rabbit out and the rabbit is waiting for you.
In a worst case scenario, Serenity and Alice may have a more hostile relationship than what’s being observed, and Serenity is going under the bed and thumping because she sees everywhere else as dangerous since Alice has the run of the place. Being under the bed may be Serenity’s attempt to find a safe place, but she’s still thumping because she feels endangered.
Best case scenario, the thumping is occurring as a way of saying, yes, I want under here please because it’s fun for me; however, if you’re saying she’s thumping while under there, I am less inclined to take this route, and more the former.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.