Out of the nine members of the Fellowship, Boromir experienced intense temptation from the Ring while more than anyone. The ring’s corruptive influence weighed heavily on him throughout most of The Fellowship of the Ring, until he eventually tried to physically take it from Frodo and… well, you know what happened next.
For years, many fans have shrugged Boromir’s struggle off as him simply having a weaker constitution than the rest of the Fellowship, but one Lord of the Rings theorist thinks there may actually be another reason Boromir felt such a pull to the Ring.
THE THEORY — Redditor u/The_Actual_Pope thinks Boromir’s corruption could have been a result of the character being poisoned by the very blood of Sauron. The redditor notes that, after arriving in Rivendell, Boromir picks up the shards of Narsil (the sword that Isildur used to cut the Ring from Sauron’s finger) and accidentally cuts his own finger on the exact part of the blade that cut Sauron. The user suggests that it’s possible some of Sauron’s own blood may have still been on the blade, and therefore, could have infected Boromir.
The theorist also notes a change in Boromir’s behavior throughout the scene, observing that he is friendly towards Aragon before picking up the sword, but distasteful and unnerved after. That could be seen as further proof that it was the cutting of his own finger — and being poisoned by Sauron’s blood — that was the source of the conflict within Boromir. If true, then that would make his death at the end of Fellowship of the Ring even more tragic than it already was.
SAURON’S INFLUENCE — Boromir being literally poisoned by Sauron does help explain exactly why he felt such a stronger pull to the Ring than his compatriots, but it’s not the only possible explanation. Both the Lord of the Rings books and the films make it explicitly clear that men as a race are the most susceptible to the Ring’s corruptive powers, which helps account for why Legolas, Gimli, and Gandalf all managed to more or less maintain their wits around the ring. Aragorn’s nobler lineage also explains why he may have had a stronger will than Boromir. The latter also suffered from insecurities and prejudices that Aragorn did not, which made him uniquely vulnerable to Sauron’s manipulations.
The evolution of Boromir’s attitude towards Aragorn throughout the scene in question also does connect back to their overall dynamic. Boromir does not believe that Gondor needs a king, and therefore, looks at Aragorn in contempt. But Boromir is also unworthy of being Gondor’s king, and him getting cut by the sword is a strong way to symbolize that in the story itself: Boromir cannot hold the sword without cutting himself, but Aragorn can.
THE INVERSE ANALYSIS — The thought of Sauron’s blood poisoning Boromir, and therefore causing the corruption that leads to his downfall, is certainly an interesting theory. However, there are already a number of in-text examples and explanations for Boromir’s connection to the Ring, which render any additional speculation ultimately unnecessary. Tolkien often used the Ring (and Sauron) to symbolize spiritual and moral corruption in the world, so it’s hard to believe he may have chosen such a literal way to manipulate Boromir.
Then again, this theory does add yet another interesting dimension to consider during future rewatches. So if you choose to make this your headcanon, there’s nothing wrong with that.