Sentence:  She knew from avalanche safety courses that outstretched hands might puncture the ice surface and alert rescuers. She knew that if victims ended up buried under the snow, cupped hands in front of the face could provide a small pocket of air for the mouth and nose. Without it, the first <WSD>breaths</WSD> could create a suffocating ice mask. 
Meaning of the word marked with <WSD> tags:  A single act of breathing in or out.