I remember reading a veterinary article complaining about the lack of research into feeding rodents chocolate; almost all existing advice, she found, seemed to be derivative of chocolate's toxicity to canines only and nothing based on anything solid.
Though I doubt Momiji or Nazrin would be affected as it's been said even at worst for chocolate to affect someone of their weight, it'd be far more than a person could stand to eat in a single sitting. And this is if being a humanoid youkai doesn't negate that.
Well, I figured as much, considering the dependence of just about any drug/toxin effect on body-mass (especially after remembering Ron White's joke about how he occasionally hid M&Ms in his dog, Sluggo's, mouth and how Sluggo is supposed to be a big dog).
That being said, I was kind of curious regarding mice. Thanks for the information, FJH!
Momiji wouldn't be affected...she is a Wolf tengu not a wolf per say. Tengu can eat anything a human can eat. Rin and Chen on the other hand....dont feed it to them