Chapter 54: why don't Harry and Quirrell cast Somnium on Bellatrix instead of deceiving her? (The deception requires Quirrell to tell Harry the Death Eater password, among other things...) Why does Quirrell talk to Bahry so confidently while Bellatrix can hear him? Why does he follow his whims to play-duel and then kill Bahry instead of quickly subduing and memory-charming him, if they planned to pull off the perfect crime? Why is he so vulnerable to Dementors that he drops immediately when Harry's Patronus vanishes, even though Bahry's Patronus is still there successfully protecting Bahry and Harry? (Or am I misunderstanding the reason for his screaming? It's very similar to Harry's screaming when he first encountered a Dementor. If the screaming were caused by Quirrell's spell coming in contact with Harry's - brother wands or whatever - then Harry should've felt a symmetrical effect, which he didn't.)

Also, am I the only one stupid enough to only now realize that the professor's name is Quivering Squirrel?