The stone gargoyle outside the Headmaster's Office was alive.
Or rather, it was sentient. It told Su Er that Headmaster Dumbledore was not in the Castle at present, and that it would tell Dumbledore someone had come looking for him once he returned.
Su Er had no system, nor anything like Occlumency supplied as a system bonus.
Of course, he knew that telling Dumbledore about the Horcrux would very likely expose many things, including his own origins.
He was gambling that Dumbledore would not dig relentlessly into a young wizard's hidden secrets, gambling that, as someone on the side of the light, he had principles and boundaries of his own.
Naturally, Su Er had looked into Legilimency, which every big shot who transmigrated into the wizarding world guarded against at every turn. It had been mentioned in that book, Advanced Magic, in the Restricted Section.
The prerequisite for casting Legilimency was that a wizard needed to look directly into the target's eyes to read their current emotions and thoughts, or stir up some of their long-buried memories.
Here, Su Er regarded it as a spell for determining whether someone was lying without needing Veritaserum.
It had many restrictions. For instance, the target needed to be unguarded, relaxed, or vulnerable; for instance, being able to see the eyes during casting made it easier to cast, and so on...
In addition, this spell could be used to extract memories and emotions.
Su Er did not doubt that Dumbledore had modified and innovated upon this spell to make it more powerful.
Nor did he doubt that Dumbledore could read his memories without eye contact.
But for the sake of his happy magical life ahead, and to protect the people he cherished, he had to take this step.
*Ideally, I could use this chance