A thin plate has a round hole whose diameter in its rest frame is D. The plate is parallel to the ground and moving upward, in the +y direction, relative to the ground. A thin round disk whose diameter in its rest fame is D is also parallel to the ground but moving in the +x direction relative to it. In the frame of the ground, the plate and disk are on course so that the centers of hole and disk will at some point coincide. The disk is contracted, but the hole in the plate is not, so the disk will pass through the hole. Now consider the frame of the disk. The disk is of diameter D, but the hole is contracted. Can the disk pass through the hole, and if so, how?