To bob something was to surgically trim or shorten it.
In 2268, following James T. Kirk's successful theft of a Romulan cloaking device and return to the USS Enterprise, Doctor Leonard McCoy asked the captain to report to sickbay so he could bob Kirk's pointy ears. Spock urged him to have the procedure quickly, as he felt that pointed ears did not look good on Humans. McCoy then asked him if he wanted to go through life resembling his first officer, which finally motivated Kirk to hurry to sickbay for the procedure. (TOS: "The Enterprise Incident")