As the previous poster has already pointed out, *if* the mouse entered your baggage after you checked it in, it was hardly LX that "allowed it in". Airlines don't open baggage (except for lost bags, maybe), rather security agencies and customs.

Or did you mean "LX allowed a LIVE MOUSE in my checked baggage" as in "LX allowed [me to check in] a LIVE MOUSE in my checked baggage"?