Nex had already been watching 173, knowing that if this 'Jack' man were to move or interupt Jeff, the statue would move and probably kill everyone, so he was staring. "Alright, I'll take your place." he said, sitting on the couch and staring at it. 
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If Jeff had moved without anyone watching 173, it would've probably moved and snapped Jeff's neck and everyone around him, but he was caught before he couldmove and inch, and was stuck as statue.