The shell has two contrasting sides, one convex, one concave; one smooth, the other ribbed. Truman uses a series of actions to actually compare the two sides. 00:11 Truman turns the shell over, convex side facing him. He pushes on the surface with his right thumb. This occurs immediately after he looks into the concave side of the shell and probes its depth with his right index finger. These two actions look like a pair, one done because of the other; one done to see how it differs from the other. These actions confirm that this paradoxical object is both convex and concave. Truman flips the shell several times, looking at it, perhaps confirming that the differences he feels with his fingers are corroborated by what he sees. He frequently changes which side is up by pronating his wrist. As Truman rotates, probes, and rubs the white shell, place this thinking both in terms of what he discovers that the shell is and what he determines the shell (or a side) is not.