Shut up again about an animal (6)
I believe the answer is:
reseal
'shut up again' is the definition.
I can't tell whether this definition defines the answer.
'about an animal' is the wordplay.
'about' becomes 're' (common abbreviation for 'with reference to').
'an animal' becomes 'seal' (I have seen 'Marine animal' mean 'seal' so perhaps 'animal' could also mean 'seal').
're'+'seal'='RESEAL'
Can you help me to learn more?
(Other definitions for reseal that I've seen before include "Close securely again" , "Close again tightly" .)