Incidentally, this reminded me of a Biblical line in which the disciples are told something like: “Behold, as I send you as sheep amidst wolves, you must be as shrewd as serpents but as innocent as doves.” I wondered how the KJ version read, but it refers to “wise” serpents, not shrewd ones. (Unsurprisingly, many different adjectives have been used in various versions of the Bible, including “cautious”, “sagacious” and “prudent”, but I have a bit of trouble picturing a “sagacious serpent,” but no trouble picturing a “shrewd” one.)
This (Matthew 10:16) is a nice example of how a text can be changed through translation.
The Greek is φρόνιμοι (frónimos), which Google Translate defines as “wise, prudent, sensible,” and is in opposition to the dove, which is ακεραιος (akeraios) which is “unmixed, free from guile, innocent, simple.”
The Latin is prudens, which has an original meaning of “foreseeing, foreknowing,” but which can mean “knowing, practiced, skilled,” and which most commonly was used to mean “sagacious, sensible, intelligent, clever, judicious.” It’s in opposition to simplex, which is “unmixed, free from guile, (morally) simple, without dissimulation, open, frank.” (It doesn’t carry the sense of “intellectually simple, stupid” that the English simple does. In medieval texts God is often described as simplex.)
Based on the Latin, “shrewd as serpents” seems to be an excellent English choice. ("Clever as serpents” works too, but you lose the alliteration.) I’m not sure if the Greek φρόνιμοι (frónimos) supports the same connotations.