New to the world of snakes

[TRD]

Well a cooled down snake may be less active but it's still a lot faster than a human... so you're still going to get tagged if you grab it by the *** (so to speak). The amount of venom doesn't really matter all that much, the neurotoxic/hemotoxic snakes usually inject enough venom to kill a human several times over, and the maiming species (myotoxins/cytotoxins in the venom) will generally inject enough of it to hurt you very badly up to the point that without support you require amputation of a limp.

The only good practice of handling venomous snakes is to keep their business end as far away from you as possible, and there are plenty of tools to do so.

But if you want your character to have a heart attack, then you could always have him grab a runaway mamba mid body, with bare hands.