"he clung to it with a fierce Pavlovian tenacity"
A reference to the work of Ivan Pavlov
(1849-1936), a Russian scientist famous for his study into classical conditioning. Pavlov performed an experiment in which he rang a bell before feeding dogs; soon the dogs began to salivate at the sound of the bell, associating the noise with food. This he called a conditioned reflex; such responses are unconscious, and automatic.