Poisonous creature causing mother to hide a bottle opener (5)
I believe the answer is:
mamba
'poisonous creature' is the definition.
(I've seen this before)
'mother to hide a bottle opener' is the wordplay.
'mother' becomes 'mam' (informal term for mother).
'to hide' is an anagram indicator.
'opener' indicates taking the first letters.
The first letter of 'bottle' is 'b'.
'a'+'b'='ab'
'ab' is an anagram of 'ba'.
'mam'+'ba'='MAMBA'
'causing' is the link.
(Other definitions for mamba that I've seen before include "one venomous" , "One's venomous" , "Deadly creature" , "Venomous snake; rhymes with dance" , "Deadly African snake" .)