Pig swallowing last of corn flakes (4)
I believe the answer is:
snow
'flakes' is the definition.
(I have seen 'White flakes' mean 'snow' so perhaps 'flakes' could also mean 'snow')
'pig swallowing last of corn' is the wordplay.
'pig' becomes 'sow' (I've seen this before).
'swallowing' means one lot of letters goes inside another.
'last of' indicates one should take the final letters.
The final letter of 'corn' is 'n'.
'sow' enclosing 'n' is 'SNOW'.
(Other definitions for snow that I've seen before include "Ice flakes" , "Slangy cocaine or other white stuff" , "Precipitation in the form of ice crystals" , "Winter precipitation a cocaine" , "White specks on screen resulting from interference" .)