the chams can not hear in the same way as humans, the low frequency can be felt by us but not heard even if we put our ear really close to the cham, the super low frequency can be just felt when transmitted thru the skin by touch, every cham keeper had this experience. the interesting thing is that most of this super low vibrations are felt by other chams from 3 to 6 m around and transmitted thru the branches of the bush or tree and absorbed by the feet of the cham, its similar to the elephants they to absorb low vibrations with their feet.
My experience regarding cham memory is by feeding a CB B. Tavetanum from hand since the 3rd month of age, now at 1,5 years of age , whenever he sees my hands close to him starts focusing to shoot the tongue.