This is a very serious issue, as rodents have been known to chew through wires. The last thing you want is to be over the Atlantic with wires shorting out and the risk of a fire...

Agreed... What seems like a minor issue could potentially turn into a major one.

For the one mouse you see, there are probably 10 others that you don't, and who knows where they are all hiding and what kind of mischief they had all gotten into. Good call on the Capt for not taking the aircraft. I'm not sure what the procedure is, but DL should have to inspect the aircraft nose to tail before letting it go out on a revenue flight.