A large Mylar sheet provides a unified surface that supports two children’s sense of shared space. Notice how the Mylar buckles into contours and makes a flapping sound when Sarah uses her feet. The thick Mylar allows the child to create a reliably repeatable shape, and when released the Mylar quickly returns to a flat sheet. The thick Mylar is responsive in ways that butcher paper, newspaper, or drop cloth would not be. Notice that the effect created by one infant—the rise and fall of Mylar waves—becomes a contagion for the second infant, as Sean energetically bangs his paintbrush up and down in an effort to imitate the motion (04:21). Later, the boy grasps the raised curve (05:06). The stout surface of the Mylar allows Sean to smear paint down the curve (05:14 – 05:17) as if to represent the motion of the Mylar. The boy then bangs the Mylar against his body (05:18) as if to create a sound similar to the one made by the girl. Sarah responds by rustling the Mylar with her feet (05:22). Together, the children use different actions to enjoy creating the same repeatable effect with the Mylar sheet.