Cough
A cough was a mechanism for expelling foreign substances from one's throat and lungs.

In 1893, Data cautioned a coughing bellboy about cholera. ()

In 2154, a silicon-based virus caused  and Hoshi Sato to have a coughing fit. Later, Doctor Phlox gave them a cough suppressant. ()

In 2366, an environmental system malfunction on the bridge of the  released toxic levels of nitrogen oxide which caused the bridge crew to cough. ()

In 2370, Geordi La Forge coughed as a psychosomatic response to seeing gases inside a ship he was exploring remotely. ()

That same year, Dr. Julian Bashir told  to cough as part of a physical. ()

In 2371, Leeta faked a cough in order to see Bashir. He "prescribed" a Fanalian toddy for her, then ordered one for himself, saying he was also feeling a cough coming on. ()

Coughing could also be a way of announcing one's presence. In 2366, William T. Riker coughed to interrupt La Forge and Christy Henshaw's romantic interlude in the turbolift. ()

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Medical conditions
Physiology