We may now have mice ...

Yesterday my SO noticed that the mouse (who is, *ahem*, still nameless) was being particularly lethargic; we barely saw her all day, and when she went to her wheel she'd just walk half a revolution or so and then give up. Today, however, the mouse has suddenly become less bulgy, and is sprinting on her wheel. She's made sure to keep the entrance to her nest box completely covered by bedding, so we can't see inside, but if we listen very carefully, every now and then we can hear high-pitched, faint little squeaks coming from the nest box.