The most common and most likely answer to this crossword clue is the 4 letter word MICE
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More clues leading to the result MICE
Buddy explains!

The straight part
We know that "Animals" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case animals = mice.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 MICE mean?
MICE noun- Any small rodent of the genus Mus.
- A member of the many small rodent and marsupial species resembling such a rodent.
- A quiet or shy person.
- (plural mice or, rarely, mouses) An input device that is moved over a pad or other flat surface to produce a corresponding movement of a pointer on a graphical display.
- Hematoma.
- A turn or lashing of spun yarn or small stuff, or a metallic clasp or fastening, uniting the point and shank of a hook to prevent its unhooking or straightening out.
- A familiar term of endearment.
- A match used in firing guns or blasting.
- A small model of (a fragment of) Zermelo-Fraenkel set theory with desirable properties (depending on the context).
- A small cushion for a woman's hair.