I think there has been confusion over the name 'butterfly adder' since pa fell off the T-rex. In the book 'Snakes alive' by Laurence Wingate the caption between 2 black and white photos of a western gaboon in the firm grip of a person's hand it states:
Two views showing the method of holding a snake's head--- in this case the Gaboon Viper or Butterfly Snake. In both cases the thumb is on top of the head and fingers well up under the lower jaw.
Although I havn't really looked, I have yet to see a B. nascicornis referred to as a 'Butterfly' snake/adder/viper.
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