Audio problem: At the end of the first flashback, Stromwell's car is shaking long before the engine revs. (00:05:40)
Audio problem: In the "previously" part, Grace whimpers "Harvey..." with a second of delay between sound and lip movement - a gap that was practically non-existent in the actual previous episode. (00:01:30)
Audio problem: When Rupert Thorne is saying "That file is here all right," his mouth is closed for the first four words. (00:18:10)
Audio problem: Alfred brings breakfast. He says "Rise and shine", but no mouth animation is included. (00:07:10)
Answer: Because he stole a chemical from his lab.
But Batman knew that with it, Clayface could permanently retain his shape and Clayface desperately wanted to be Matt Hagen again. In a sense, Batman stopped Clayface from becoming human.