One of the reasons both publishers and fans appreciate having Whelan covers on their favorite books is that he creates an image which both calls out to buyers and accurately interprets the story. For CATSPAW by Joan D. Vinge, his portrait of the main character Cat does all that.
When Cat takes a certain seductive and addicting drug, his latent psi abilities enable him to sense other people's thoughts. To heighten his powers, he becomes hooked on the drug which he administers to himself via a skin patch behind his ear. Cat is always checking to see if the patch is there, and Michael posed him that way to suggest his nervousness about coming down from the drug as well as the idea of him listening to other people's thoughts.