The most common and most likely answer to this crossword clue is the 3 letter word EEK
I've seen this crossword clue in The Times
E
E
K
Buddy explains!
The straight part
We know that "that’s scary" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that’s scary = eek.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 EEK mean?
EEK verb- To produce a high-pitched squeal, as in fear or trepidation.
- Representing a scream or shriek (especially in comic strips and books).
- Expressing (sometimes mock) fear or surprise.
- Representing the shrill vocal sound of a mouse, rat, or monkey.
- Face
- Also