gut reaction

go with one's gut

To trust or follow an intuition or instinct, as opposed to an opinion based on a logical analysis.

gut check

An honest, reflective appraisal of one's true feelings concerning a matter of concern.

gut factor

The emotional dimension of decision-making. A person's subjective (often almost visceral) feelings about what is right or wrong, good or bad.

gut feeling

An instinct or intuition; an immediate or basic feeling or reaction without a logical rationale.

gut out

To endure stoically.

knee-jerk reaction

An instantaneous reaction made without thought.