Packing tape hardly glides off the spool—it hiccups and jerks, only to release a prodigious ribbon that needs to be cut down to size. Now, researchers have used slow-motion, microscopic video to explain the physics underlying this sticky mystery, Physics Today reports. The videos showed that the longer the tape got stuck the more tape it unspooled when it slipped, the team reported earlier this month in Physical Review Letters. Researchers used those observations to create a mathematical model that fits their measurements of the tape’s sticks and slips. The model also predicts that the tape peels up from what it’s stuck to from side to side, like a wave, and not as a uniform front. Future research will seek to explain why, at the microscale, the tape seems to peel sideways.