A Strannat was a creature used on Kanvia to ascertain whether someone is telling the truth or not. Strannats could sense brainwave patterns and were particularly sensitive to the nervous wave changes (aka cognitive dissonance) that beings produced when they lied; furthermore, Strannats possessed a barbed tail and could be easily trained to kill those they sensed lying. An extremely disciplined mind could fool a Strannat and speak lies without danger.
A Strannat was used by the Rinic family of Kanvia to ascertain whether John Crichton was planning to destroy them or not.