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Hammer a nail into a tree, and it will get stuck. So why doesn’t the same thing happen to the sharp beaks of woodpeckers? Scientists say they finally have the answer.

In a new study, researchers took high-speed videos of two black woodpeckers (Dryocopus martius) pecking away at hardwood trunks in zoos and analyzed them frame by frame to see how the head and beak moved throughout each peck. The bird’s secret: an ability to move its upper and lower beaks independently, the team reports this week at the virtual annual meeting of the Society for Integrative and Comparative Biology.

Once the tip of the woodpecker’s bill hits the wood, the bird’s head rotates to the side ever so slightly, lifting the top part of the beak and twisting it a bit in the other direction, the videos reveal. This pull opens the bill a tiny amount and creates free space between the beak tip and the wood at the bottom of the punctured hole, so the bird can then easily retract its beak.

Until now, scientists have thought woodpecker bills would need to be rigidly attached to the skull to successfully drill into the wood to find insect prey. But actually, the bill’s flexibility in these joints ensures that the bird’s signature “rat-a-tat-tat” doesn’t stop at “rat.”