Two Mouths, One Place

Some levels have no line home through open space: a wall with no gap, or a plant behind the chute.

Two places that are one

A wormhole joins two places. A rock that crosses into mouth a is shifted by the offset from a to b: it lands beside b exactly where it was beside a, at the same speed and heading. That spot is within b's sphere, so the next step, 1/120 s later, would shift it straight back. A latch shuts b to that rock until the rock is clear of it.