When Aubry didn't player her shot in the dark, Ozzy should've known he needed to play his Idol
He saw her as an obvious enough boot to start jury managing to her face. So at tribal, when she doesn't do the one thing she can do to save herself (playing shot in the dark) it means there's something else going on (especially with the shots in the dark expiring soon)
A savvy player in Ozzy's spot (like Rachel back on the Operation Italy season) would've played their shot in the dark to see if they needed the idol. But at a bare minimum, when Aubry doesn't try to save herself, that's the single most obvious sign that Ozzy needs to play his idol
Plus if he makes it to the final seven, Ozzy + Rizo + Cirie + Extra Vote can at minimum force rocks, so this is the best spot to play the idol. You also know Rick Devens is probably playing his idol in the other tribal, so if you play yours Jeff probably hides at least one new idol that you Rizo and Cirie can look for (but maybe you're assuming Rick Devens is 100% to find it first)