Revealing mistake: At the beginning, Lional's limo comes to a screeching halt on railroad tracks. The camera is panned out to where you can see this happen. The black tire marks that are supposed to appear from the hard braking are already present, which means there were multiple takes.
Smallville (2001)
1 mistake in Mercy
Martha Kent: Clark? What are you still doing out here?
Clark Kent: Well, I'm still doing my chores.
Martha Kent: Well, you usually finish those in about two minutes. How is it that I drove to Metropolis, attended the Children's Foundation dinner, and made it back before you finished?
Clark Kent: Because I'm doing them the normal way.
Trivia: When Clark confronts the Flash in his hotel room, he reads off the fake IDs Jay Garrick, Barry Allen and Wally West. Those are the secret identities of the first three men to be called the Flash in the comics. Also, this Flash says his name is Bart, like Bart Allen, the teen hero formerly known as Impulse and currently being called "Kid Flash." (00:10:35)
More questions & answers from Smallville
Answer: No, there is no such character in the comics. He's a "meteor-freak" like all the other baddies on the show. The sound has something to do with him vibrating his vocal cords very fast to create a high-pitched squeal.