Quote from Frasier in Travels with Martin
Martin: We don't have a rabies certificate for the dog. Guard: I knew something was going on here. Martin: Yeah, well you see, we weren't planning on coming here, and when we got to the border we just forgot all about it. Niles: And I for one, didn't even know that you needed one. Frasier: Yes, but ignorance of the law is no defense so take the little dog away and we'll be off!