Continuity mistake: At Ryan's surprise welcome back party, Clark puts his right hand over Ryan's shoulder as he asks him "you knew about this didn't you?" Cut to a different angle as Ryan responds "I was tempted too" but now Clark's hand is no longer on Ryan's shoulder. Cut to Clark then back to Ryan and now Clark's hand is back on Ryan's shoulder.
Plot hole: Mayor Tate and Lex have a discussion about bribes and Tate says this is his 4th term. In last season's episode "Crush", Pete gets a job as a summer intern on Mayor Spiegel's re-election campaign. So how is it possible for Tate to have been on his 4th term when in the previous year Spiegel was Mayor?
Continuity mistake: After Clark finds out that Ryan is dying, we see him holding a comic book in the farm. His dad then arrives and he turns to look at him. He places his left hand to his side as he holds the comic book in his right hand. Cut to a different angle and now both his hands are together in front of him.