IN SIDE OUS = INSIDIOUS<br />
Thats my guess. Josh has something Insidious is trying to get "inside" him in Chapter 2<br />
and something insidious is trying to get "inside" of Dalton.
Inside us, Demon is a puppeteer and we are the puppets. Marionettes and puppets in his room suggest this also. He <br />
wants to be inside us.
It was their slogan if you will for the trailer. Insidious IS Insidious. The words would flip forwards and backwards and the IS would remain. I have no idea why they chose that as their slogan though.
I think si is an abreivation as u kno he falls asleep. So the answer is SHUT IN. See