In his hallucination, Malcolm is once again faced with opening The Box, saying the girl inside is suffering, and Martin mentions that Schrodinger might disagree. Schrodinger was a quantum physicist who posited a famous thought experiment named for himself, concerning a hypothetical cat in a sealed box. Briefly put, Schrodinger's Cat can be thought of as existing simultaneously as alive and dead while inside the sealed box, as its status as either alive or dead wouldn't be possible to confirm until the box is open.
The hotel in this episode is based on the infamous Cecil Hotel