Jim putting the stapler in a meatball is a callback to putting the stapler in jello
When Robert is looking at pictures of his house he's about to put on the market Jim initially jokes that it looks like the house from The Shining. Robert says he when he bought the house, he hoped it would be house like in Eyes Wide Shut. Both of the films referenced were directed by Stanley Kubrick
This is the first episode to show Cathy's attraction to Jim, albeit subtly.