In theory: the pupil and Sana going in and out of possession could hint at Pareidolia not being as effective at possession as others.
Notably, after that Event:
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Pareidolia shows up, introduces itself, and "helps" Sana in:
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While she's seeing things and USER1 is seemingly Account Sharing:
Which may imply that something can hack into the stuff of other USERs/gods. Pareidolia seems like the prime suspect considering at least one Narrator fears it, and it's notably able to do what others can.