Drinking, bathing, washing, swimming, etc.
or
Because they only know their ABCs "Anybody But Clinton".
or
The question is irrelevant, since you couldn't find the dolls even if you knew how many. (Note: Well, this was a good joke in 1983-84. . . .)
or
When it came time to pay, the skunk didn't have a scent, the deer didn't have a buck so they put the meal on the duck's bill.
or
They turn from notating nuclear spins to notating unclear puns.
or
2 years old.
Cow: "Mooooove over"
Sheep: "Naaaaaaa."
or