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He can't block peter from getting his ability. Peter only need to understand how it works to be able to use it.
Actually, he's used powers before without even knowing he had them. Just this previous episode he used super speed without even knowing anyone around him had it and he's done this as far back as the first few episodes of season 1 with flight.
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I think it makes sense. He knows how his own ability works, and he knows how Peter's works. It's just natural that he can keep others from accessing it.
I agree with this theory, its the only one that makes sense.