Well -

I said this in the PTP thread but:

Jupe's "show" was new to an audience - but he'd been working at it for 6 months (which is when the Keith David character was killed) - and was how long the non-moving cloud was in the sky.

He'd been buying horses and sacrificing them to the monster, while "training" it for a show without a crowd. That's what the Daniel Kaluuya character was seeing in the distance (the lights and music) that the horses would run toward. Which is also why Jupe was cagey when pressed for a plan to buy the horses back ("yeaah....").

So this was the first time with an audience - he was passing out the flyers that it was a 'new' family show, and why the actress who was mauled by Gordy was there. It was essentially the premiere. And he didn't factor in that there were all these people there and that variable is mirrored by the first scene on set where the horse kicks up and acts violent on stage for the commercial. The people attending the show (or just on set doing their jobs) don't have that agreement with the animal - and so it just went nuts and attacked them.

As for why he thought he could control it - I think that's the point to all the monkey backstory. Now, did the monkey ACTUALLY have a connection with him? We don't know. Could have been that the bedsheet was actually shielding his eyes from him. But still - Jupe was misguided, clearly.