Underground Fortress (Part 1)
Every time Lith made a mistake, the Rezar would accumulate the missed air bubbles around Lith's mouth and nose, forming a cushion that helped him catch his breath and stop his coughing fit.
'Dammit, moving through the earth is much harder than swimming underwater like the merfolk taught me.' Lith thought. 'Moving works almost the same but breathing is an entirely different matter.
'Merfolk have gills that allow them to extract oxygen from water and could pass me as much air as I needed just by taking deeper breaths than usual. Underground there is no air, instead, and Nalrond has to keep a low-pressure area to draw oxygen from above and then split it between us.
'We are akin to two divers with only one oxygen tank so we can't waste any. In his Rezar form, Nalrond can hold his breath for a long while but he still needs to breathe just like me.