It's obvious that he lied because Comey has a tell. He's not a masterful lier like some of these people. Pause, look up and to the right, repeat the question. There were other times he legitimately had to pause to answer a question thoughtfully and his body language was completely different. He would tell us why the question was complicated and took some though in a straight tone when he was being honest. He would be high pitched otherwise.

He got really uncomfortable with the perjury line of questioning. He didn't lie there but he was hoping to think of one. Luckily each of the questions were simple enough he couldn't get around those. You can see some of the pausing there.