I was told that this one is "abuse disguised as a joke," so I figured it might belong here.
In a discussion in mesechta succah about an esrog that had some nibbling on it, the gemara explains that even if you say that an esrog that a person has bitten a piece off of is still kosher, if a mouse nibbled on it, it's passul, because "achbar mice-y."
OK, technically, it's more like "achbar mi'isi", but still...