More than just those big buck teeth! Jackrabbits actually have twenty-eight of the suckers: for the upper row, there are 4 incisors (one main pair and one secondary pair behind the main one), 6 premolars, and 6 six molars, while the bottom row have 2 incisors, 4 premolars, and 6 molars. What a mouthful!
Source: http://fieldguide.mt.gov/detail_AMAEB03050.aspx (Tip: learn how to read dental formulas--it's very easy, go to wikipedia to find out how. Then you can Google an animal's name and the term "dental formula" and find out the number of teeth in a lot of different mammals.