Cortana is definitely going to want to keep an eye on that remaining rat going forward-even if there aren't any more effects from the bread, she's also curious about things like whether being exposed to the supernatural really does increase the likelihood of it happening again and whether that's true for animals, how well it recovers and does it have any lingering issues, etc.

There was someone else who was keeping rats, yeah? Cortana might want to keep it with those rats or in a similar arrangement.