Chemical crypsis in the puff adder Bitis arietans.
Crypsis is a means by which animals avoid detection by predatory or prey animals. Visual crypsis is blending in with the background, background mimicry or camouflage. Chemical crypsis is the lack of emitting odor or the emitting of odor indistinguishable from the background.
The puff adder is a large, heavy-bodied, venomous snake from Africa that catches its prey by hiding in ambush. It employs visual crypsis-- background mimicry-- to avoid detection by prey and predatory animals the latter of which are 42. Fifteen of these predatory animals rely heavily on odor detection, and a puff adder emits virtually no odor thus reducing predation by these animals.
The means by which the snakes obtain chemical crypsis is unknown, and rigorous tests employing dogs and meerkats have shown that they have great difficulty in detecting puff adders by odor.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4707760/