Is "breaths" grammatically correct?

In some books, I see the use of the word "breaths" in the phrase "they held their breaths". Is this correct? And if it is, should I go by the Ngram (below) in spite of grammaticality?

http://ngrams.googlelabs.com/chart?content=held+their+breath%2Cheld+their+breaths&year_start=1800&year_end=2000&corpus=0&smoothing=3

Or are both correct? (If so, I would go with the more popular "held their breath".)

Solution 1:

The singular form is correct in this context:

Bob and Alice held their breath.

As is:

The crowd held its breath.

But "Bob tried to quiet his breaths" would also be correct.

Solution 2:

Depends on if 'breath' is considered an indivisible noun in context. 'They carried sand' vs 'They carried sands.' Both are correct, both say something different.

'They combed their hair' vs. 'They combed their hairs'. Both fine, emphasis is different.

'They received money' vs. 'They received monies'. Each correct, each different.

'They saw the light' vs. 'They saw the lights'. Correct, different.

Finally, 'They held their breath' vs. 'They held their breaths'. One emphasizes unity of action, the other implies individual actions. Both are grammatical.