the beating refers to the overusing of the "dead horse". Said horse is a metaphor for a joke, and the fact that it's no longer living implies that it's no longer funny
person1:hey...is that a dead horse
person2:uhhh.....yyy..yes i believe it is...why do you ask?
person1:oh no reason...say...you wouldn't wanna beat that dead horse would you?
person2:i thought you'd never ask
persons1+2 proceed in beating the dead horse
five minutes later, cop enters
cop:hey are you beating that dead horse?
cop:...well...care if i join you?
persons1+2:not at all
cop starts shooting horse whilst the tho persons continue to beat it with sticks, fade to black, THE MORE YOU KNOW enters along with someone from Friends talkin' about some stupid crap.THE END...But is that really the end?...Yes, yes it is...Or is it?