Venomous types putting two and two together? (6)
I believe the answer is:
adders
I believe this is a double definition.
'venomous' is the first definition.
(type of snake)
'types putting two and two together?' is the second definition.
(people who add up)
(Other definitions for adders that I've seen before include "Re Dad's snakes" , "sum? We do" , "Arithmetic snakes?" , "Snakes are totters" , "Totting snakes" .)