Dolemort sat relaxedly in the backseat of the car while Mr. Clark had taken the driver's seat. Most of the time when Mr. Clark accompanied Dolemort to any important appointments, he would drive the car for him because there were usually some important confidential business discussions between them. Dolemort didn't like letting any third person hear it, even if its his own driver, thus as his Chief Secretary and his beta, Mr. Clark had been always mindful of it.
Similarly, after walking out of the restaurant after meeting Elena and her father Mr. Smith, Dolemort possessed an overwhelming silence which started to make Mr. Clark feel a bit anxious.
Usually, Dolemort would initiate a few conversations with Mr. Clark right after any appointment was over, but even after he had driven for almost 30 minutes, Dolemort didn't speak a word to him.