BOB (3)

Bob, v. i. 1. 1. To have a short, jerking motion; to play to and fro, or up and down; to play loosely against anything. “Bobbing and courtesying.” Thackeray.
2. 2. To angle with a bob. See Bob, n., 2 & 3.
He ne'er had learned the art to bob For anything but eels. Saxe. To bob at an apple, cherry, etc. to attempt to bite or seize with the mouth an apple, cherry, or other round fruit, while it is swinging from a string or floating in a tug of water.