[Dagny Taggart] thought of the evening last winter, when [Hank Reardon] came in, took a small package from his pocket and held it out to her, saying, "I want you to have it." She opened it and stared in incredulous bewilderment of a pendant made of a single pear-shaped ruby that spurted a violent fire on the white satin of the jeweler's box... [the stone looked] like a sparkling drop of blood.
On the other hand, when Cheryl Taggart finally realized how evil her husband Jim was, she visited Dagny to discuss the matter. They emphasized their connection to each other and discussed philosophy, with Dagny calling her her "sister... by choice" (not through Jim, as emphasized by Cheryl).
Upon returning home, she discovered the fact that Jim had just had an affair with Hank Reardon's wife. She confronted him on that as well as his "overall" evil, demanding to know why he had married her in the first place. At the end of their confrontation, she concluded that
"You... you're a killer... for the sake of killing..."
It was too close to the unnamed; shaking with terror, [Jim] swung out blindly and struck her in the face.
She fell against the side of an armchair, her head striking the floor, but she raised her head in a moment and looked up at him blankly, without astonishment, as if physical reality were merely taking the form she had expected. A single pear-shaped drop of blood went slithering slowly from the corner of her mouth.
In the second scene, Jim's evil is on full display, ultimately expressing itself in physical abuse of his wife. This is an expression of the basic violence and destructiveness of his philosophy as well as of his personal evil.
In the former scene, Hank Reardon gives Dagny a gift simply for the pleasure of seeing her wear the pendant. It's a reflection of his love of life and the depth of their feelings of each other. It is reflected shortly thereafter in a physical expression of that (in contrast with the second scene, where this is the result of a physical expression of Jim's evil and his feelings of contempt for his wife).
Was this deliberate on the author's part? Did she intend these scenes to be parallel, or was this purely coincidental?