The answer is frog. Otto Meyerhof used frogs in his research on muscle metabolism. By studying the muscles of frogs, Meyerhof was able to make significant discoveries about the biochemical processes involved in muscle contraction and relaxation, for which he was awarded the Nobel Prize in Physiology or Medicine in 1922.
The Fascinating World of Otto Fritz Meyerhof: A Quiz on the Life and Contributions of a Renowned Physician and Biochemist