You usually see "as sly as a fox."
The phrase "sly as a fox" is a simile because it directly compares Max to a fox using "as." If it were a metaphor, it would say, "Max is a fox."
Since there is no "like" or "as" in the sentence, it is a metaphor.
simile
his fox paw craftily stole the biscuit
He was a fox, and could outsmart everyone.
It is a similie as you are comparing (something) to how sly the fox is. A similie uses the words "like or "as".
he was a sneaky jackrabbit.
Since the phrase uses "is," it classifies as a metaphor.
he is a fox
It is a similie as you are comparing (something) to how sly the fox is. A similie uses the words "like or "as".
a metaphor uses like or as
He used a metaphor to desciribe the swaying trees.