This episode has two plots: the giant jackrabbit and Beverly Caterers. The jackrabbit portion is funny, but the telephone exchanges between the Clampetts and Beverly Caterers are comedy gold and the funnier of the two plots. (The Clampetts think that Beverly Caterers is a poor "widda" woman who cooks for others out of the goodness of her heart.) What makes these phone calls so funny is that we only hear the Clampetts' side of the conversations, and it's clear that the woman on the other end of the phone thinks she's talking to crazy people and is probably using lots of expletives to tell them to stop calling and pestering her.
These farcical misunderstandings is what makes The Beverly Hillbillies so funny, especially in the early seasons, when the Clampetts were still learning about the idiosyncrasies of "city living."