From The Nonverbal Dictionary of Gestures, Signs & Body Language Cues, published by the Center for Nonverbal Studies Press in 2000.
SOLITARY DINER’S GLANCE
Gaze direction: The tendency of a lone diner a. to look up in a café or restaurant, and b. to move the eyes horizontally across the view-field while taking a bite of food or drinking from a cup, bottle, or glass.
Usage: Solitary diner’s glance resembles the cautious visual checking that goes on among unacquainted individuals (e.g., in elevators and waiting rooms), though it occurs at regular intervals (usually with each bite or sip) and with greater frequency. The behavior may be a protective response to stranger anxiety.
Research Report: Eibl-Eibesfeldt (1970) observed that individuals who ate alone looked up and around into the distance after each bite or two, alertly “scanning the horizon” against enemies, much as baboons and chimpanzees do in the wild.