When viewing Orson Welles sitting in the chair from behind, his cigar has no smoke coming from it. Next shot when viewing Orson face on, the cigar has smoke coming from it.
During the coroners inquest, Trent was seen drawing a sketch of Marlowe. This is not allowed in English Courts. Although court artists are allowed in as members of the public, all drawings must be done by memory outside the courtroom.
To test his theory that the killer was a good actor, Trent says he's contacted the vice-president of the dramatic society in Oxford, who told him Marlowe gave a good performance as Mercutio in Hamlet. But Mercutio is a character in Romeo and Juliet, not Hamlet.
When Trent reads the first part of his report, it ends with three dots. However his finger movements never made the action of hitting a key three consecutive times at the end.
When John Marlowe impersonates Sigsbee's voice on the phone to sell all the shares, John McCallum appears to be using his own voice. However when Marlowe is on the phone impersonating Sigsbee inquiring about the fictitious George Harrison, its obviously Orson Welles' actual voice dubbed. The two voices in each occasion are different when they should sound the same.
It has been suggested that Trent's reference to Marlowe playing "Mercutio in Hamlet" was a character error. However, if you listen carefully, Trent does not say " Mercutio IN Hamlet"; he says that, at Oxford, Marlowe "had played Mercutio AND Hamlet brilliantly." There is no error.
As Marlowe begins to tell his story to Trent and Cupples, there is a flashback to watch his story played out. In the flashback, Marlowe packs his suitcase and leaves the Manderson house to get the car. Then Sigsbee Manderson speaks privately with his wife Margaret. That conversation is not logically part of the flashback, because Marlowe wasn't present to hear it, and the flashback is exclusively Marlowe's recollection of events he witnessed.
Sigbee Manderson seems to be the most right handed lefty in the world. Espicially the way he doesn't handle his cigar.