The most common and most likely answer to this crossword clue is the 3 plus 4 plus 1 plus 5 letter word EAT LIKE A HORSE
I've seen this crossword clue in The Times
E
A
T
L
I
K
E
A
H
O
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S
E
More clues leading to the result EAT LIKE A HORSE
Buddy explains!
The straight part
We know that "Use a nosebag/scoff heartily?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case use a nosebag/scoff heartily? = eat like a horse.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.