Late to the party as usual, but what @anon65652885 said!
They can trap air in their drysuit feet/legs specifically and look “pinned” upside down. Love the effect of them gathering air; inside caves your air on the ceiling looks just like shiny mercury gliding around the rock formations (pic below), and they use that effect here with light reflecting on the floor.
Loved when they released the wheelbarrow and “balloon” which then drifted off to the depths above (below).
It definitely chills me to the core thinking about it, only because even in a drysuit, that water is super damn cold!
