Orr had a seizure in the vicinity of the parasite that had infected Harry Fletcher, Dawn Shale, Jack Harkness and two others. They repeatedly changed forms before Mr Colchester was able to calm them down. (AUDIO: Love Rat)
In North Carolina in 2002, a group of cheerleaders all suffered identical seizures with no obvious physiological cause. Oliver Morgenstern researched the event as an example of mass hysteria. (AUDIO: Hysteria)