Once upon a time, there lived a young wide-mouthed Frog who dwelt in a swamp. He was a very inquisitive young Frog, and drove his parents to distraction with endless questions. Then one day, having reached the age of majority, he set out into the world to seek his fortune.
Off down the road he hopped: Hopitty hopitty hop, just like that.
The very first day, he met a Wildebeest. He'd never seen a Wildebeest before. He hopped up to Mr. Wildebeest and said, "Hello there, Mr. Wildebeest! What do you eat?"
The Wildebeest looked at him with sad, ancient eyes, and replied "I eat fungus, Master Frog. Day after day, fungus."
The young wide-mouthed Frog replied "Oh! Thank you very much." He bade the Wildebeest a good day and hopped on down the road.
The following morning, our intrepid Frog met a Shoat. His hopped up to the Shoat, hopitty hopitty hop, just like that, and he asked the Shoat: "Hello, Mr. Shoat! What do you eat?"
The Shoat stared at him for a long time, in a very cold way. Finally the Shoat cleared his throat, and spoke sharply:
"Swill. I eat swill. I assure you, your opinion of my diet does not interest me in the least. Good day." And the Shoat turned on his heel and stalked off down the lane.
"Well," said the wide-mouthed Frog to himself, and called after the Shoat: "Thank you very much, Mr. Shoat!" The Shoat gave no sign of having heard.
So the young Frog hopped on, and hopped and hopped. Toward evening, as the shadows grew long, he noticed an Ocelot sitting very still and silent in the shade of an old tree, watching the road with wild unblinking eyes. The Ocelot saw the Frog, and he smiled a broad and toothy smile.
The Frog hopped no closer, but stood his ground and spoke to the Ocelot.
"Hello, Mr. Ocelot! What do you eat?"
The Ocelot's smile grew broader, and he said very gently, "Why Mr. Frog, it's funny you should ask. I eat wide-mouthed frogs."
And the Frog pursed his lips as if eating a lemon and replied, in a very tiny voice, "oh."
I learned this joke in the Boy Scouts, many long years ago. The punchline works a lot better when told in person, because you can act it out instead of describing it.