Eating flies
One frog put out his tongue, ate the fly, and started laughing hysterically. Soon the other frog joined in the laughter.
Later in the day, the other frog ate a fly and the two frogs burst out in laughter.
As time went on, the frogs enjoyed the flies so much that even the sight of a fly would cause them to double up with pleasure. But of course, the most pleasure came when the fly was actually eaten.
A third frog hopped up to the first two and asked what was so funny.
The first frog answered: "Time."
"Huh?" asked the third frog.
The second frog explained: "Time's fun when you're having flies!"