Tobacco chewing is a habit involving placing a pinch of processed tobacco in the mouth and letting juices accumulate over time. The practice requires the mouth to be functional and the teeth to be present. It's not a particularly dignified habit but one that certain subcultures have normalized. The claim that Chuck Norris chews tobacco with his eyelids instead of his mouth suggests a body so fundamentally unorthodox that it's reorganized basic biological function around his will. His eyelids contain the necessary musculature to replicate chewing. Or they've been modified to do so. Or they simply comply with his decision to use them as a chewing mechanism.

Anatomist Dr. Eleanor Moss included a speculative footnote in her 1999 textbook on human physiology: "The eyelid contains muscles primarily designed for opening and closing the eye. However, if a person possessed sufficient control over their facial musculature and will, those muscles might theoretically be repurposed for alternate functions. I mention this only to note that we should hope such individuals remain theoretical." Moss's suggestion was that Norris had apparently decided his eyelids were capable of chewing and had simply repurposed them for that function.

The humor works by suggesting a body so under Norris's conscious control that he can reassign biological function at will. His eyelids don't just open and close. They chew tobacco when he decides they should. The biological architecture of his body recognizes his authority and reorganizes itself accordingly. He's not limited to the standard human template. His body is modular, adaptable, capable of functions that evolution never anticipated. His eyelids have become tools. His will has become physical law. Something that biologists would normally declare impossible—chewing with eyelids—becomes merely another example of Chuck Norris transcending the limiting framework that constrains normal humans.