Stone pillars appear in Aquatic Ruin Zone. When Sonic approaches a noticeably short pillar (shorter than himself), the pillar rises to its true height, barring Sonic's way. Since the top of the pillar is just within the reach of his jump, Sonic must Spin Jump onto the top of the pillar, which breaks in half upon impact.
Stone pillars also appear underwater in the same Zone. Sonic can jump on top of them to access a shortcut, but if he misses, he falls to the bottom of the underwater area. When Sonic approaches an underwater pillar from below, the bottom half of the pillars falls to the ground. These stone chunks can crush Sonic if he is going at the wrong speed.
When Knucklesplays this zone since his jump height is slightly lower than sonic's, unless he manages to somehow get a little more height he will be unable to reach the top of the pillar and as a result, be stranded on the current side of the pillar.