Even as Lex fought against the dentist, his disadvantage still pretty significant, he continued to pay attention to his surroundings as well. He did not believe, even for a second, that there was just a dentist randomly waiting inside the jungle, past the barrier, for him to arrive.
It was much more likely that the dentist was summoned, or maybe even created, specifically as a result of his actions. Maybe he was finally being punished for taking things from the jungle.
That meant there was still a possibility of more such enemies popping up out of the shadows. There was also the fact that his instincts were so clearly guiding him that the dentist hid the secret to following Fenrir.
