All sounds are vibrations. But high frequency vibrations that can't be felt, will not be heard by snakes. The frequency must be low, non-directional sounds like bass.
Hm.. This is a bit odd, but I'm synesthetic (I can see certain sounds) and I've noticed that the snakes can seem to 'hear' the sounds that I can see. Pretty much anything low pitched or like... Certain noises that are both loud and clear enough to resonate, like a violin vibrato or something. Though those are probably also strong enough to cause vibrations that can be felt
Lora i was taken aback by your comment about seeing sounds this sounds fascinating any further information would be greatly appreciated.
I'm not actually a gynecologist...but i'll take a look.