For my own part I think that Cain's version is infinitely more humorous and instructive as well, because a "door is not a door" when it is a "daw," which is, indeed, as Cain's answer to the riddle claims it to be, a bird.

It is, of course, a great compliment to Cain that the Senator and a hundred others I might name like him should go back to him for their humor, but I think they would do better if they took his jests exactly as they found them instead of trying to improve them to their destruction.
I find also in our family records that it was Abel who first asked the question, "Why is an elephant like an oyster?
Because it cannot climb a tree," a jest that similarly to Cain's riddle, possesses not only true humor but is at the same time educational, as the best humor must always be, in that it teaches the young certain indubitable facts in the Science of Natural History, viz., that neither the pachyderm nor the bivalve, in common with several other carnivorous botanical specimens, is gifted similarly to the squirrel, the ant, or the grizzly bear.
Mother Eve, who always took a naive delight in the droll sayings of her offspring, used to tell with great glee of Cain's persistent habit of asking questions of his father, some of which used to tax all the old gentleman's powers of invention to answer intelligently.

One of these that I recall most vividly was as follows: "Say, Pa," said Cain, one Saturday afternoon, when the whole family were off on a picnic together, "did you have any sisters ?" "No, my son," replied Adam, plucking a bottle of olives from a neighboring tree, and placing them on the outspread table-cloth on the grass.
"Well, did Ma have any sisters ?" persisted Cain.
"No," said Adam.

"Your mother had no sisters, either.

Why do you ask ?" "Oh, nothin'," replied the lad with a puzzled expression coming over his face as he scratched his back.