The Snails will dig through the sand without showing any visual difference. Each block they pass through gets closer to overloading PLMs. In order to Power Bomb the left wall before PLMs are overloaded, it is necessary to only allow one snail to dig, either by bombing one or by facing one to prevent movement until it is off screen. If using mobile G-mode, it is easiest to get past the bottom one and prevent it from digging. If using immobile G-mode, it is easiest to have whichever one hits Samus go off screen. It is important to place the Power Bomb while as far right as possible to ensure that PLMs have not been overloaded before breaking the wall, or, wait until the snail has fully overloaded PLMs and dug a small place where Samus can unmorph against the wall to place the Power Bomb before quickly unmorphing and exiting G-mode. The green stone changes one tile earlier than the wall, and can be used as a visual cue to place the Power Bomb. Note that the Snails will not dig while off screen or while Samus is facing them, even while she is morphed.