 In "Small Favor", it is indicated that Mouse, in addition to comprehending speech, can show emotion on a level with humans - when told to "take the catnip away" if it makes Mister sick, he seems to indicate doubt; when Thomas claims that what he said earlier about Harry was a joke, Mouse merely flicks his ears and turns away.Also, when Harry jokes about shaking himself dry like Mouse in Michael Carpenter's home, Michael responds that Mouse would be too polite to do so inside and is promptly proven correct.In "Changes", Mouse is proven to have intelligence as great as any human, and in correct circumstances the ability not only to comprehend human speech but also to communicate as well as any human in his own language.