Perhaps the rarest opening defense is the Hippopotamus Defense (1.e4 Nh6), also known as the Adams Defense. Still, it's a playable defense in reply to any move that White may make on his first move. Over the years, I've collected about 200 games with this defense and recently co-authored a book on this defense with Davide Rozzoni (original editor of Unorthodox Openings Newsletter (UON)) and Gary Gifford (current editor of UON and problem master at Chessville.com). The book, Winning with the Krazy Kat and Old Hippo, has over 160 games with the ...Nh6 defense. The book is available from Lulu Publishing at http://www.lulu.com/content/3292224 . John C. Thompson of England played this defense and used the hippo name for his system and a booklet he published in 1957, called the Hippopotamus Chess Opening. The opening defense was later popularized by Dutch master Philip Du Chattel (1945- ). We called the variation with the Black Knight on f7 and the Bishop on g7 the Krazy Kat. We called variations without the Bishop on g7 the Old Hippo. A true hippo would be 1.e4 Nh6 2.d4 g6 3.c4 f6 and ...Nf7. I've played ...Nh6 dozens of times as Black and feel comfortable with it. Here is one of my games in which the witch doctor tried to put a spell on me after I tried to play a hippo defense (perhaps not a true hippo unless ...f6 and ...Nf7 is played). But I turned the game around and checkmated the king in the middle of the board. Be sure to click on Move List for other variations, Krazy Kats and Old Hippo games using this defense.