Cataloguing

Cataloguing was a process that was once used by Judoon law enforcement to identify different species. When employed on the residents of Royal Hope Hospital, it separated humans from non-humans.

This process was used by Judoon who were trying to locate a criminal, Florence Finnegan, a plasmavore who could mimic human biology, who was hiding among humans in a hospital on Earth. The Judoon scanned each lifeform's head, marking the humans who had already been scanned with a black "X" on the back of their hand.

Martha Jones showed traces of non-Human DNA (that of the Doctor) which caused the Judoon to do a "full scan." When she was proved to be human, she was given some sort of voucher for "compensation." (TV: Smith and Jones)