Wind can pick bacteria up from the ground and bring into the sky, sometimes settling in  clouds thousands of feet above us. Sea spray can also send bacteria flying. The mystery has been, how does rain do it? Now, mechanical engineers writing Wednesday in the journal Nature Communications say they've figured it out. It has to do with tiny bubbles.

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"I don't want people thinking they shouldn't go outside after it rains because they might get some bacterial infection. I definitely don't want people thinking that," says Cullen. Melioidosis, he says, is very rare. And, if rain really is the culprit behind a small rise in cases, that would only be the case in the rare locations with exactly the right conditions — and with the disease-causing bacterium living in the soil. "Bacteria, unfortunately, get a bad rap," says Buie. Most, he says, are harmless or even beneficial. And sometimes they even smell good.