"Njord," Bildin yells through his hat, "get us through these vines!" He fumbles through his head for a way to help Njord. Actually trying to slash the vines with his dagger might expose him to poison. He could cast a spell with one hand, but what could he do? Fire would just make it more difficult to get through, and the gas may be flammable. Shifting the earth would be complicated, messy, and probably wouldn't work anyway.
Actually, any type of physical exertion would cause him to breathe faster. He's trying to conserve breath, not waste it. He didn't want to end up like Njord. Bildin looks at Njord; he looks ill.
Wait, he could try to seal off the cavern. The poison holes were behind them. If they continued forward, the poison would probably follow them. "Physical exertion," part of Bildin thought. "The poison. Don't forget the poison," another part thought.
Njord would have to cut their way through. Bildin can't help him with that. Instead, Bildin decides to separate them from the source of the gas. Turning around, Bildin holds his hat to his face with his left hand. With his right hand, he summons ethereal power from inside himself. He feels his respiration speed up as he does so. With a burst of power, Bildin wills the ceiling in front of them to collapse, isolating them from any new gas.
