Fig. 1. Video frames from a swallowing sequence illustrating (A) the normal position of the eyes; (B) head extension and lordosis of the vertebral column during initial eye retraction; (C) full eye retraction and (D) a kinematic trace of the percent eye retraction versus time for the same swallowing sequence. The arrows in D, labeled A, B and C, correspond with the frames from the swallowing sequence. Note that eye retraction is rapid, the eyes remain retracted for a relatively long time, more than 0.5 s in this example, and then eye protraction is slower than eye retraction. A representative video of Rana pipiens swallowing a cricket can be viewed online (http://jeb.biologists.org/).