Things went from perfectly okay to really bad in the span of a few seconds.
There was nothing down there. The tunnel was hard to view, narrowing past a few feet, but there was absolutely no sign of their guide, nor any sign he'd ever been there. But right as Marcus asked how things were, the ground beneath him shifted, and the trap sprang closed.
To Marcus, all the thick purple plant matter began to move at once, and then the top of the tunnel which Ferris had just hopped into snapped shut, squeezing so tightly together that it was barely clear that there'd been a tunnel there at all. Then, the upper part of the plant went still, leaving Marcus safe and unharmed... but also outside the tunnel.
Ferris was in a far more dire situation.
Having just hopped directly into the mouth of the plant, he was effectively in its throat, and as the top closed up, the entire throat contracted, squeezing down on him. The tunnel went from giving him plenty of space to no space at all, with almost no room to move or squirm, seven feet below ground level.