Spirit tells me that action expresses thought more honestly than words alone usually do, when it isn’t designed to pretend to express thought.

How could action pretend to express thought?

Seemingly spontaneous actions can be skills that have been practiced until they have become almost instinctive responses to situations they have been designed to respond to.

Can sincerity become a skill?

No.

Then how can it be recognized?

By the degree of consistent harmony.

Between?

Actions expressed and the unspoken thoughts.