The most common and most likely answer to this crossword clue is the 4 letter word HOBS
H
O
B
S
Buddy explains!

The straight part
We know that "ferrets" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ferrets = hobs.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.
What does HOBS mean?
HOBS noun- A kind of cutting tool, used to cut the teeth of a gear.
- The flat projection or iron shelf at the side of a fire grate, where things are put to be kept warm.
- The top cooking surface on a cooker; a cooktop. It typically comprises several cooking elements (often four), also known as 'rings'.
- A rounded peg used as a target in several games, especially in quoits.
- A male ferret.
- The hub of a wheel.
- A fairy; a sprite; an elf; a bogey.
- A countryman; a rustic or yokel.