THE BIG BANG THEORY Season 6 Episode 17 The Monster Isolation Photos : “The Monster Isolation” – After a terrible date, Koothrappali vows to never leave his apartment. Meanwhile, Penny actually impresses Sheldon with her acting skills, on THE BIG BANG THEORY, Thursday, Feb. 21 (8:00 – 8:31 PM, ET/PT) on the CBS Television Network.