What's That Smell?

A couple of days ago, a coworker was scanning groceries and came across something uncanny. Someone had picked up a jar of alfredo sauce who knows how long ago, screwed off the lid and put it on the shelf. Over time, the contents of the jar congealed in the form of chunky mold. As my coworker was running the jar over the scanner, the lid came off, spilling a small amount of the contents. A smell enveloped the front end of the store for a while, and the mess was quickly cleaned up, but an hour later a customer asked me what the smell was and put her coat over her nose. Today, I checked in that checkstand and could occaisionally make out The Smell, which was lurking in no particular place.