Is open-mouthed about the right berries (6)
I believe the answer is:
grapes
'berries' is the definition.
The definition and answer can be both things that one consumes for nourishment as well as being plural nouns.
Maybe they are linked in a way I don't understand?
'is open-mouthed about the right' is the wordplay.
'is open' becomes 'gape' (as in to gape open).
'mouthed' becomes 's' (I can't justify this - if you can you should give a lot more credence to this answer).
'about' means one lot of letters goes inside another.
'the right' becomes 'R' (common abbreviation).
'gape'+'s'='gapes'
'gapes' going around 'r' is 'GRAPES'.
Can you help me to learn more?
(Other definitions for grapes that I've seen before include "Source of wine" , "Vine fruit" , "They grow on vines" , "Fruit for wine" , "'Green, black or purple clusters (6)'" .)