The puff adder is an extreme sit-and-wait predator. Individuals may remain in one ambush position for days, which solves the problem of being seen but creates another: a stationary animal has time to accumulate a scent plume that predators can follow.
In experiments in South Africa, dogs and meerkats trained to locate snakes by scent found other species reliably but performed no better than chance on puff adders held in the same conditions. The result has been interpreted as chemical crypsis, an apparent reduction in the volatile cues that scent-tracking animals use, and it is the clearest evidence of such an ability in a reptile.
The mechanism is not established. Whether the snake produces fewer volatile compounds, produces different ones, or simply lacks the chemicals these particular trackers are tuned to has not been resolved, and the finding rests on a small number of studies. What is certain is behavioural: the species does not flee, which is why so many bites follow an unnoticed step.