Um. They live in phlegm, or saliva, or other bodily secretions, and can be passed along from person to person. They cause diseases."
He peered around for an example and summoned the Mobile Phone Number Five. With a surgical scalpel, he scraped a needlepoint-sized bit of unidentifiable grey fuzz off the fingerprint-covered frame and presented it to Caractacus, putting it under the light of his workbench.
"Try Engorgio on this as far as you can take it, then use the strongest lens you have for the examination. Look for something very small, in groups, usually round or rod-shaped."