In one study, zacks et al. (2009) recorded someone making a sandwich and asked participants to press a button when they thought one action was complete. the results of the study indicated that indicative of the end of an action.

I believe the answer is: Changes in speed
Average people tend to become more focus and accelerate our effort when we're on the brink of finishing a certain goal.
So in the scenario above, when a sudden tense/increased movement happen in our body the researchers could perceive it as we're on the brink of finishing an action.

Ifeel like this means that we shouldn't just live for ourselves.also, we should respect others as well as people around us. it reveals that everyone should have equalized freedom, no matter their differences: races, cultures, skin color, etc,. we all deserve the same privileges.