Painting, say, expression of enjoyment in hold, performing acrobatics (12)

'painting' is the definition.
Although both the answer and definition are present participle verbs, I can't see how one could define the other.

'expression of enjoyment in hold performing acrobatics' is the wordplay.
I cannot really see how this works, but
'expression' could be 'whee' (I have seen 'Expression of delight ' mean 'whee' so perhaps 'expression' could also mean 'whee') and 'whee' is found within the answer.
'in' is found in the answer.
This explanation may well be incorrect...

'say' acts as a link.

Can you help me to learn more?