[mcswell]

Still looking for hen's teeth, but they seem to be as scarce as chicken breasts. (The only breasts found so far are on mammals.)

[card_zero]

"On February 29, 1980 (enough of a rarity in itself), E.J. Kollar and C. Fisher reported an ingenious technique for coaxing chickens to reveal some surprising genetic flexibility retained from a distant past."

-- Stephen Jay Gould, Hen's Teeth and Horse's Toes

Two pages of technical explanation follow, but they got chicken embryo tissue to produce teeth.