The thing that I find most people cannot understand is that each snake has a distinct personality. This is something people only associate with mammals and birds, but from someone who has studied venomous snakes firsthand and puff adders (Bitis arietans) in particular, I can judge how each snake will react after spending time with them, and some are curious, some bold, some aggressive and some are even timid. To take it a step further, in my studies with our own adder (V.berus), I've got to know certain individuals so well, that I can pick them up with bare hands. Although you have to judge what mood they are in that day, because their moods can change like any other animal.
As with all animals though, wild specimens can be unpredictable and I wouldn't recommend anyone try it.