In Reed’s director’s commentary for “Ant-Man and the Wasp” (which you can listen to on Disney+), he discussed why he inserted the clip from “Animal House” early in the movie. According to Reed:

“As we were talking about the quantum realm, and the idea that there could be worlds upon worlds down there in the subatomic realm, I remembered that scene from Animal House where they’re talking about, you know, [chuckling] ‘Entire universe could exist in my fingernail.’ So, we were able to license that clip from Universal and just have it as a little Easter egg in the background.”

The scene in question centers on Donald Sutherland’s hip Professor Jennings smoking marijuana with Boon (Peter Riegert), Katy (Karen Allen), and Pinto (Tom Hulce), who’s never partaken before. He’s the one whose mind is thoroughly blown by the possibility that he could be housing an entire universe in his fingernail — which prompts Pinto to ask Jennings if he could buy weed from him. Sutherland’s reaction to this request is a perfect capper to the scene in one of the funniest movies ever made (one that Warner Bros. thought would never work).

It’s a bit of dumb fun in a franchise filled with amusingly stupid antics. Reed’s superhero trilogy has its own brand of randomly funny bits as his characters, much like Pinto, contend with the bewildering expanse of the Quantumverse. Thankfully, no one accidentally kills a horse in any of the “Ant-Man” movies.