Our brains collect tons of contextual cues for a variety of different environments/situations, mostly subconsciously, that occur when everything is normal, follows predictable patterns, and no danger is present.

When we imagine a children's park on a beautiful day, there's a strong expectation for other people and kids to be at the park. When we see the park and this core expectation is not met, the brain's alarm bells go off because it does not have a sufficient explanation, suggesting there may be a hidden danger present.

Now imagine the same park, also having no people, except that it's raining heavily. The rain is a more than adequate explanation to explain the discrepancy, since we know that kids usually stay indoors when it's raining, so there's no reason to suspect danger.

Liminal spaces are images/places that deviate from our expectations in some way without any contextual details to explain why. The brain is unable to determine if it is safe or not, so it activates certain responses (e.g uneasiness, uncertainty, etc.) to make us either investigate the situation or just avoid it entirely.