Aah knew I was missing something. I thought it was hinting that the platform we could see was actually a box of snakes so I didn't want to jump on it haha.
So I'm having a bit of trouble again at the rescuing Leah level. The tutorial said when you're touching the wall, she can move through it but it seems a little inconsistent? Sometimes I push up against the rightmost wall and Leah can walk through, sometimes she seems blocked completely no matter what I do, sometimes I die to the spikes and she can suddenly walk through the floor upon respawning without the black box moving at all.