When Jimmy Olsen is fighting with Butler on the ledge, Jimmy's bow tie is neatly tied. Butler then makes Jimmy fall from the building, possibly to his death. Superman quickly flies by, catching Jimmy and saving him. Moments later, Superman brings Jimmy into Kent's office by the window to safety. Jimmy's bow tie is now untied and draped around his neck.
When the Human Bomb takes Lois out on the ledge of the Daily Plant building, the shot of the street below shows a large two-tone truck driving down the street. When Jimmy goes out on the ledge several minutes later, they again show a shot of the street with the same distinctive truck driving by.
Twice while in Perry White's office, White asks Jimmy if he's inferring something, e.g., "Are you inferring that Kent can do anything I can't do?" White is mistakenly using "infer" when he actually means "imply." Infer is what a person thinks to themselves, while imply is what they say to someone else. White should've asked, "Are you implying that...?"
When Butler explains his plan to control Superman, he's holding a fixed gaze at the camera indicating that he's reading his lines from cue cards.
Superman's ruse is to trick Butler into thinking he's always present by having his profile in shadow and playing a recorded response if spoken to. However, at any time Butler could have demanded to see Superman in plain sight or come to the window.