The snake used in the advertisement? (4,5)
I believe the answer is:
puff adder
'the snake' is the definition.
(puff adder is a kind of snake)
'the advertisement?' is the wordplay.
I cannot quite understand how this works, but
'advertisement?' could be 'puff' (I've seen this before) and 'puff' is located in the answer.
The remaining letters 'adder' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'used in' is the link.
Can you help me to learn more?
(Other definitions for puff adder that I've seen before include "Venomous viper" , "Large viper" , "Poisonous type" , "Snake" , "African viper" .)