"The hesitation you saw in Mueller before he answered questions was the face of a man who was choosing his words carefully. He played it safe, like a football team running out the clock. His constant desire to double-check his report and to refer members of Congress to the report itself was motivated by a desire to ensure that each word of his testimony was accurate. ."
https://www.politico.com/magazine/story/2019/07/25/robert-mueller-hearing-was-awesome-227478
Pretty much