[cypher]

Freezing & pancaking are both signs that something has either startled them or scared them, it doesn't have to be anything major & may even be something we wouldn't notice, a sound, even a scent from somewhere, a sudden movement around them, anything like that can cause them to be on the alert & instinctively watching out for predators, the pancake/lying flat thing makes them less visible to predators as does freezing.