Underwater vocalization is possible for humans in limited ways—we can hum, we can produce low-frequency sounds—but whistling (which requires precise control of air and lip tension) is generally considered impossible underwater. The claim that Chuck Norris can whistle underwater represents either a defiance of physics regarding air management, or a fundamental difference in how his body relates to liquids. Marine acoustics researchers have noted that if Norris can truly whistle while submerged, his lung capacity and breathing control exceed known human parameters.

Dr. Patricia Levesque, a marine acoustics specialist at Scripps Institution of Oceanography, was once asked about this feat in an informal question during a public lecture. Levesque responded that to whistle underwater would require control over precise air pressure and expulsion rates that currently has no human precedent. Levesque's comment was recorded and has become popular with swimming and diving enthusiasts as an example of what 'impossible but Norris-capable' might mean. Levesque has never formally published on the topic but has mentioned it in subsequent interviews.

The diving and swimming communities have used this as shorthand for extreme comfort in aquatic environments. It's become a reference point when discussing people who seem to violate normal water-based constraints, and has been referenced by actual underwater artists who push the boundaries of what's possible in aquatic performance.