I recently watched the first Harry Potter movie and noticed a pretty big plot hole.
As we know, Snape turns over once Lily Potter dies and runs to Dumbledore for help and becomes a spy ultimately. Yet through the remainder of Voldemort's life, he believes that Snape is on his side yet he should have found out in the first movie.
As we know, Quirrell for the entirety of the first had Voldermort on the back of his head, living and breathing off him which means, shouldn't he also hear everything too?
When Harry and Quirrell are with the Mirror of Erised, he tells Harry that Snape was trying to counter curse his broom during his Quidditch match. Quirrell also gets confronted by Snape in the hallway (when Harry was snooping in the restricted section) telling him, he needs to figure out where his loyalties lie.
My question is, why didn't Voldermort hear Snape talking to Quirrell, figure out he was on Dumbledore's side and kill him once he rose?