Snakes like having second thoughts (4)
I believe the answer is:
asps
'snakes' is the definition.
(asp is a kind of snake)
'like having second thoughts' is the wordplay.
'like' becomes 'as'.
'having' means one lot of letters go next to another.
'second thoughts' becomes 'ps' (as in a PS in a letter).
'as'+'ps'='ASPS'
(Other definitions for asps that I've seen before include "Pass (anag)" , "Poisonous creepers" , "Poplars" , "native Africans?" , "Poisonous snakes" .)