In the scene where Willard is in his bedroom closet, he is trying to block the hole that Ben has created. On a closet shelf there is a Christmas Decorations box. The exact same box can be seen on a shelf behind his boss in the office supply room.
When Willard's boss is working on his spreadsheet program, just before the rats show up, he is not entering the spreadsheet formula properly. He is entering the actual numbers like 235+345+315 instead of using cell addresses like =A1+B1+C1. Not really a mistake because his character could be an idiot on spreadsheets. Just an interesting observation.