How are they running out of oxygen if they’re breathing it right back into the submarine?

Commentary:
Well, it appears this submarine is playing a classic game of hide and seek with oxygen – breathe in, breathe out, oops where did it go? 🌬️🤷‍♂️ Seems like they need a lesson in keeping track of their precious gas or it might end up being a case of "One breath in, two breaths out, one oxygen tank gone!" 🤦🤣