Source of bait that's a big issue? (3,2,5)
I believe the answer is:
can of worms
'big issue?' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'source of bait that's a' is the wordplay.
I cannot quite see how this works, but
'of' could be 'o' and 'o' is found within the answer.
'bait' could be 'worm' (bait when fishing) and 'worm' is present in the answer.
'a' could be 'an' and 'an' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for can of worms that I've seen before include "nasty problem" , "What may prove problematic" , "this may turn out awkward" , "amateur angler's bait?" , "Bird's convenience food" .)