More than a novelty than anything else with a tiny derringer .22 short. The little gun will have enough umph to most likely do serious injury and maybe nick an artery and produce life threatening injury if shot with it.
I can kill squirrels with .22 shorts out of my Henry.
Might make for an interesting variation on darts, a "parlor gun" of sorts. Try to be safe with it if you make the decision that shooting guns indoors is a good idea because it probably isn't.