Good ears! Very healthy. Must have been living with you for a while! He looks like the classic Yankee woodpile mouse to me, an opportunistic occupant of homes as well. His cousins will have declared Vendetta and now must be plotting revenge.

Bernd Heinrich writes:

"According to Mason A. Walton, the so-called Hermit of Gloucester, who in 1903 wrote about them in his book, A Hermit's Wild Friends or Eighteen Years in the Woods: 'The white-footed mouse, unlike the house mouse, is a handsome fellow. He sports a chestnut coat, a white vest, reddish brown trousers, and white stockings. His eyes and ears are uncommonly large, causing his head to resemble a deer's in miniature. This resemblance has bestowed upon him the name of "deer-mouse."' (p. 118)

"Deer mice juveniles have lead-gray pelage and white bellies. Unlike meadow voles or field mice, they also have long legs that allow them to bound like deer. There are, however, two species of closely related deer mice, and only one of them is the official deer mouse, Peromyscus maniculatus. The other is the white-footed mouse, Peromyscus leucopus.

"Differences between the two species are subtle. One field guide I consulted indicated taht in white-footed mice the tail is longer than the body, while in the deer mice it is shorter. But those that I measured at my cabin had tail lengths about equal to their body length. Only experts [and other mice] can distinguish between the two, and the defining characteristic used for differentiating them is a molecular vairation in their salivary amylase, an enzyme in their saliva that helps digest starch. [Heinrich discusses the claim that only P. leucopus carries Hanta virus.]

"Even with Hanta virus out of the picture, deer mice can be objectionable in a cabin, and in the winter they enter in droves. I can't blame them though. The fault is mine. I should have used dry, nonshrinkable ceiling boards to foil these partly arboreal mice. Nor should I have used Styrofoam panels for ceiling insulation. I had not been warned that Peromyscus systematically shreds Styrofoam into chips. The chips drift down like unmeltable snow through cracks between the boards and fly up into the air when one tries to sweep them up. The mice, once inside, also raid one's dry goods, and use one's shoes, and bed, to hide them in. The Hermit of Gloucester, who lived before the age of Styrofoam, had dozens around him simultaneously. He was entertained by them, yet even he acknowledged, "A few mice for company on winter evenings would not be objectionable, but I draw the line when I am forced to eat and sleep with them." Relocating them, Walton learned, had little effect. One night he caught twenty-eight mice in his cabin and released them a mile distant. The whole crowd returned by the second night, noisily announcing their presence with the drumming of their tiny feet (a sound now familiar to me). Deer mice, which utter no vocal sounds perceptive [sic] to our ears, use these drumrolls to communicate messages to one another---messages that remain undeciphered by man."

I can't believe you didn't let him keep the cake. After you gift-wrapped it, too.

I have been told that amount of whiteness on underparts and length of tail are indicators of different species, but clearly that's wrong, if Heinrich says so.

The house must have a good hole or crack somewhere, fairly close to ground level. Inspect before your shrubs (if any) leaf out. There's a type of foam stuff they can put in the holes around your foundation where the mice are getting in---it really does deter them. Or is there a gap under the door?

One sign a house has mice is that when snow falls, little bumped-up tunnel networks appear. Mice burrow under the snow for grass seed. When they can't get cake.