Here is the passage again:

Diane picked at the slice of cheesecake with her car keys. While Nick sucked whipped cream off his fingers. Horrified, Rachel watched her roommates decimate the dessert that she had spent three hours preparing.

The second part is a subordinate clause fragment. Although it has a subject, Nick, and a verb, sucked, the subordinate conjunction while keeps it from expressing a complete thought.

Go to the next passage.

HomeTermsExercises MOOCHandoutsPresentationsVideosRulesAboutShopFeedback