Frost tells W.P.C. Hunter to get out of uniform and into plainclothes as he wants her help on the university case, but he has no authority to do so. He would need permission from the uniformed duty inspector first to "second" her for any length of time (or the duty sergeant at the very least for the shift she is already working).
When Frost is in the professor's office, he examines the bookshelf. First, there are two copies of the same book ("Psychology") just a few inches apart, Next, when Frost removes a book called "Violent Death" and opens it, it's clear that a phony cover was placed on a real book upside-down.
The sound effects are louder than the spoken dialogue on this episode on Roku streaming in 2024.