It’s definitely a part that requires a trained animal, and the dog that plays Charlie does a wonderful job.
The dog Ken Marino singles out, Charlie, is the one that is paired with Adam Pally’s character, Dax, in the film.
Dax is a lazy, irresponsible layabout, and he finds his lifestyle upended when his sister (Jessica St. Clair) and her husband (Thomas Lennon) have twins and need him to take care of their pet.
It’s a problematic situation because Dax lives in a building with a “no animals” policy, but also because Charlie is the kind of dog who does what he wants when he wants to: he’ll flop right on top of Dax at a random moment, take forever on walks sniffing things, and wake him up early in the morning.