When mum's holding a bottle opener, it can be dangerous! (5)
I believe the answer is:
mamba
'it can be dangerous' is the definition.
The definition suggests a singular noun which matches the answer.
'when mum's holding a bottle opener' is the wordplay.
'when mum' becomes 'mama' (synonyms. I am not sure about the 'when' bit.).
'holding' means one lot of letters goes inside another.
'opener' suggests taking the first letters.
The first letter of 'bottle' is 'b'.
'mama' enclosing 'b' is 'MAMBA'.
Can you help me to learn more?
(Other definitions for mamba that I've seen before include "It may be deadly" , "serpent" , "One's venomous" , "Venomous snake; rhymes with dance" , "one venomous" .)