Second try; my replies go out into the ether.
David,
I'm not sure it will answer your son's question, but I wrote a little Mavens
Word of the Day column about lambs and their tails back in 2000, when Random
still Housed Reference. You can find it at
http://www.randomhouse.com/wotd/index.pperl?date=20000407
Best,
Enid
Lexicographer - Editor (still)