Corrected entry: One of the first times Willard takes the rats out in the bags, he says Ben can't go because if he gets in the bag, no one else will fit. Well when we see Ben in the bag later, it is clear that there is still quite a bit of room left in the bag to fit at least five more rats in there.
Corrected entry: As Willard goes through the house rat proofing, he duct tapes the toilet lid down, but when Catherine uses Willard's toilet, the duct tape he used to secure the lid is cut so she can just lift the lid.
Correction: She does tear off the tape to get it open. you even hear a ripping sound..
Correction: Willard is just using that as an excuse because he doesn't like Ben.