In literature, “sly” often conveys a subtle blend of cunning, mischief, and secretiveness. Authors use it to hint at a character’s inner guile or to suggest that beneath a seemingly innocuous smile or glance lurks a more devious intent. For instance, one character is described with a sly demeanor that adds playfulness to his words (“she’s a sly cat” [1]), while another bears a sly, suspicious expression that underscores his untrustworthy nature ([2]). In other passages, a sly smile or glance is employed to inject irony or to reveal an undercurrent of scheming, as when sarcasm and hidden mockery are communicated through a brief, almost conspiratorial look ([3]). This layered use of “sly” enriches character portrayals and infuses the narrative with a dynamic tension between appearance and intent.