Of Unknown Origin (1983, CDN/USA) C-89m. **½ D: George Pan Cosmatos. Starring Peter Weller, Jennifer Dale, Lawrence Dane, Kenneth Welsh, Shannon Tweed. Weller plays a manager-type yuppie, who wants to spend a few days without his family in their N.Y.C. apartment. However, a giant rat has found its way up, and Weller's attempts to get rid of it will turn the flat into a battlefield. Some cleverly directed sequences highlight picture, although credibility is abandoned early on. OK of its type. Based on the novel by Chauncey G. Parker III. Produced by Pierre David.