the conversation between McGonagall and Quirrell

This isn't relevant to your comment here, but I was amused in the light of recent events by the following remark in that conversation:

"James Potter," said Professor Quirrell, his eyes narrowing. "The boy is not much like James Potter. [...]"

Back on topic:

Quirrell's plot is to manipulate Harry into a certain mental state, which is directly related to the gesture he made to McGonagall

Maaaaybe. But in that conversation it seems to me as if the mental state he's referring to and gesturing at is something like "determination to do away with death by all means possible" and while Q might be bluffing when he indicates to anyone who'll listen that Harry's attempts are likely to have diastrous consequences, I'm more inclined to take him more or less at face value there.