Visitors to the San Diego Zoo got a special treat today when Henrietta, one of the zoo's hippos, laid an egg. Lead biologist at the zoo, Dr. Kimberly Luntz, stated that this was, indeed, a very rare occasion as only one other hippo in captivity ever laid an egg. Few people realize that the hippo, along with the platypus and spiny ant eater, are part of a group of egg laying mammals known as "monotremes". Proud mother, Henrietta, certainly seemed surprised when she lay the egg, as evidenced by her reaction in the video posted below. She will have to wait six months for her new baby to hatch, though, according to Dr. Luntz. Link: http://www.latimes.com/dp-top10.aprilfools.pg.0401-photogallery.html