There is an ant walking across the dining room table. It is carrying what looks like a breadcrumb. The crumb is about the size of the ant’s head. I put a pencil across the path of the ant. The ant bumps into the pencil, turns left, then right, then bumps into the pencil again. It tries to clamber over the pencil, but I roll the pencil slightly, preventing the ant from getting over the barrier. It turns right and continues on along the pencil toward the eraser end. I put down another pencil, making a corner to fence in the ant. It continues on along the length of the second pencil. I move the first pencil to the other end and continue boxing in the ant. When it traverses the third side, I move the second pencil over to the last side. When the ant has completed all four sides, I pick up one of the pencils and tap the crumb with the sharp tip of the pencil. The ant drops the crumb and scurries away, but encounters the remaining pencil on the table.