filtration, flirtation

Flirtation or flirtation means behavior meant to attract romantic attention; or trifling with someone's affections --
She seems interested in what he's saying, but it's really just flirtation.
He is given to flirtation; don't take him seriously.

 Flirtation may also mean a brief spell of  interest in something; trifling or dalliance --
After a brief flirtation with modern literature, he majored in business and was quite successful.

Filtration or filtration means removing impurities by straining liquid or passing air through a paper or cloth device, or through sand, charcoal, or some other substance --
If filtration isn't practical, we might need to boil the water.
We need to call a specialist to look at our filtration system.

Now that you know that, you can say --
"He thought she was winking at him, but it wasn't flirtation; the filtration system was bad and the smoke bothered her eyes."