Seymour puts the blackmail note in the left hand desk drawer, which is otherwise empty. Later the detective removes it from the right hand drawer, which is full of papers.
At 18:25, Muriel is shot dead and her eyes are closed as she falls to the floor. Around 19:10, Seymour and the maid go into the room together. They find Muriel dead on the floor. When Seymour rolls her over, her eyes are wide open. After the camera pans out, you can see one of her eyes closed again.
When Seymour pulls gun on his Aunt, initially,the gun's hammer is not cocked. The very next view the revolver hammer is cocked.
When Aunt Muriel is shot, her eyes are closed. When her body is "discovered", her eyes are open.