While conducting a separate experiment, the scientists learned that a virus was living in the mouths and throats of a good portion of the people in the study, a virus that the researchers didn’t think was capable of infecting humans. Worse still, it seemed to be slowing some of the subjects’ mental abilities, especially their ability to process visual information.

Surprising to researchers was that a microscopic organism that we thought could infect only algae — plants — was living in about 40% of the small number of people tested.

For the rest of us, the bigger surprise may be that this virus could join the ranks of microorganisms that live inside and on us, changing the way we think.