Slowly [Frodo] drew it out. Bilbo put out his hand. But Frodo quickly drew back the Ring. To his distress and amazement he found that he was no longer looking at Bilbo; a shadow seemed to have fallen between them, and through it he found himself eyeing a little wrinkled creature with a hungry face and bony groping hands. He felt a desire to strike him.
'No, no!' cried Frodo, snatching the Ring and chain from Sam's hands. 'No you won't, you thief!' He panted, staring at Sam with eyes wide with fear and enmity. Then suddenly, clasping the Ring in one clenched fist, he stood aghast. A mist seemed to clear from his eyes, and he passed a hand over his aching brow. The hideous vision had seemed so real to him, half bemused as he was still with wound and fear. Sam had changed before his very eyes into an orc again, leering and pawing at his treasure, a foul little creature with greedy eyes and slobbering mouth. But now the vision had passed. There was Sam kneeling before him ....
No one, as far as I can recall right now*, has remarked on what might be another instance of this same phenomenon. To be sure, it is easily overlooked, embedded as it is within Frodo's reaction to Boromir's actual attempt to seize the Ring. By contrast, Sam was not trying to take the Ring, and Bilbo, though yearning to see and touch the Ring again, reads Frodo's reaction and repents of even asking to see it so quickly, that it's hard to see his reaching for the Ring as hostile. Consider the following:
His fair and pleasant face was hideously changed; a raging fire was in his eyes.
Terror and grief shook [Frodo], seeing in his thought the mad, fierce face of Boromir, and his burning eyes.(FR 2.x.399-400)
So, perhaps we should see Frodo's perception of Boromir's face here in the context of his clearly Ring-induced perceptions of Bilbo and Sam, and allow that the image of Boromir's face that Frodo had in his mind was not entirely accurate. For, if Frodo sees threats to the Ring where there are none and momentarily perceives those he loves as evil creatures, will he not experience the same distortion of his vision when the threat is real, as it is with Boromir.
* Please let me know if someone has made this comment before. I would love to see it.