In light frame construction, a birdsmouth joint or bird's beak cut is a woodworking joint that is generally used to connect a roof rafter to the top plate of a supporting wall. It is an indentation cut into the rafter which consists of a "seat cut" and a "heel cut" or "plumb cut", forming a shape resembling a bird's mouth. The indentation should not extend unsupported on the interior in order to maintain the structural integrity of the rafter because the unsupported section can split along the grain of the wood. The joint is generally fastened with nails by toenailing the rafter from the side into the top plate below.