I try to remind myself that there are perfectly fine reasons for this to occur. For example, the person might suffer from insomnia. They might have a lower functioning brain due to developmental issues. They may have been in an accident which caused brain trauma. They might operate on a wavelength sufficiently different from you in that moment such that communication seems impossible, and you perceive that as their deficiency rather than a mutual problem.

The reasons to be compassionate are far more realistic and numerous than the possibility of a person being a zombie. It’s best to assume they have a story and a reason attached to their current state that, given time to consider, you would probably relate to them easily.