Don't Look For A Reason... Look For A Way Out
Why it is hard sci-fi
A handful of strangers wake inside a lattice of cubic rooms, some trapped. The film commits to one rigorous mechanic. The lattice has a coordinate system, the rooms shift on a schedule, and the trap distribution can be computed from the room numbers. The mathematician character derives the rule on screen. The science is procedural and the horror is in the shape of the proof.
Science inside it
Number theory and modular arithmetic. The room coordinates encode whether a room is trapped, then the rule extends to factor coordinates by primes, and finally to permutations. The film is one of the few thrillers built around a working mathematical puzzle the audience can follow.