Mammal sitting next to her unopened egg? (6)
I believe the answer is:
ermine
'egg?' is the definition.
The definition and answer can be both animals as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'mammal sitting next to her unopened' is the wordplay.
'mammal sitting' becomes 'mine' (I can't explain this - if you can you should give a lot more credence to this answer).
'next to' means one lot of letters go next to another.
'unopened' means to remove the first letter (without opening letter).
'her' with its initial letter taken off is 'er'.
'mine' after 'er' is 'ERMINE'.
Can you help me to learn more?
(Other definitions for ermine that I've seen before include "Stoat in northern regions" , "Animal with brown fur that turns white in winter" , "Fur trimming on royal robes" , "garb for nobility" , "White fur associated with judges" .)