I have pet rats, and one of them once figured out that I kept the trashcan in a cabinet under the kitchen sink. I figured out that he realized this when I discovered him inside the trashcan. The cabinet bottom stuck out a bit over the floor and he'd chewed a hole through it then jumped into the can.
Coach FinstockFirst off, rats will solve this problem in short order, they're incredibly smart, and "rat sightings" is an absolutely hilarious metric. As we all know not seeing a rat means there are no rats, right?