Big Bang Theory Stills

Leonard (Johnny Galecki, pictured second from left), Sheldon (Jim Parsons, pictured far right), Wolowitz (Simon Helberg, pictured second from right) and Koothrappali (Kunal Nayyar, pictured far left) undertake a challenging and dangerous experiment, attending the Halloween party being thrown by their hot neighbor, Penny (Kaley Cuoco, not pictured) on The Big Bang Theory.

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