The most common and most likely answer to this crossword clue is the 6 letter word SIDLES
I've seen this crossword clue in The Daily Telegraph
S
I
D
L
E
S
More clues leading to the result SIDLES
Buddy explains!

The straight part
We know that "Sneaks" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sneaks = sidles.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 SIDLES mean?
SIDLES noun- An act of sidling.
- To (cause something to) move sideways.
- In the intransitive sense often followed by up: to (cause something to) advance in a coy, furtive, or unobtrusive manner.