airangel429
Armed & Dangerous
IF SNAPE IS SKILLED AT OCCLUMENS...THEN HARRY MAY VERY WELL BE HAVE POWERS IN LEGILIMENCY...READ BELOW...FROM HP LEXICON.
"'Don't lie to me,' Snape hissed, his fathomless black eyes boring into Harry's. 'Boomslang skin. Gillyweed. Both come from my stores, and I know who stole them.'" (GF27)
Harry had been ignoring Snape's needling up to that point, until Snape finally goaded him into meeting his eyes. Unfortunately for Snape, he and Harry are having different conversations at this point without realizing it. If he'd continued to press Harry on these points, the whole business of the undercover Death Eater at Hogwarts could have been blown open right then - but the conversation doesn't play out that way.
Harry believes the mention of boomslang skin to be a reference back to the CS11 incident in his second year, and doesn't know anything about any more recent thefts of it from Snape's private stores, so Snape could not have learned anything about the more recent incident by using Legilimency on Harry here.
As for the gillyweed, the logical thing for Snape to have suspected up to this point was that Harry took it himself, not that anyone took it for him. Even if he learned through Legilimency that Dobby took it for Harry, Harry at this point is not thinking of how Dobby learned about the gillyweed, so Snape couldn't have learned it from Harry just by Harry's reaction to this question.