Violet's hand jumps from her neck to her mouth when she tells the doctor that Sebastian had been looking for hungry birds.
When Dr. Cukrowicz talks to Mrs. Venable about Sebastian's purity, she is looking at him, but after the cut (just before he asks whether she wants to see Catherine) she is instantly looking away from him.
When Catherine enters the walkway over the men's ward, she turns halfway towards the railing and holds it with her left hand. During the long shot she turns further and holds it with both hands, but then the next medium shot resumes from her previous position.
The doctor's hands change position when he tells Hockstader that he needs more time.
The plant referred to as "The Lady," is incorrectly referred to as a Venus flytrap when it is actually a pitcher plant.
Violet Venable says that the dinosaurs were vegetarians and that is why they died out. Not all dinosaurs were vegetarians (e.g., T. Rex), and even in the time of the film people knew that. However, Violet Venable is not the brightest person and tends to believe that reality is whatever she finds convenient.
Although set in 1937, costumes, hairstyles and makeup worn by Dame Elizabeth Taylor are all contemporary in 1959.