I wonder who invented gum.
It must have been hard for them to introduce the concept to people:

"It's like a snack, but don't swallow."

Everyone probably made fun of that person for awhile.
Then they got fed up and thought of a snappy comeback to all the gum taunts.
They probably said something like,

"Fine go ahead and chew on your own cud, like a cow.
I'll be over here chewing on this gum I just invented instead.
I'll see you cows later. Moo!".

Then eventually everyone got sick of being mooed at by the gum inventor.
So they were like,

"Fine, jack-ass we'll have a piece. Just stop your mooing."

Then they liked it and it caught on.