Voldemort is the last known Parselmouth, so it would be highly suspicious for Quirrell to also be one.

When Salazar Slytherin invoked the Parselmouth curse upon himself and all his children, his true plan was to ensure his descendants could trust one another's words, whatever plots they wove against outsiders.

• You have two parents, four grandparents, eight grandparents, etc.
• A generation is 20-25 years (depending on how young people have children)
• Salazar Slytherin lived one thousand years ago.

In short, today either every wizard in Britain is a descendant of Salazar Slytherin or none is. It seems awfully convenient for Quirell to suddenly have a foolproof way to make Harry believe certain claims. It seems to me that the whole "snakes can't lie" thing would have been revealed when Quirell was trying to convince Harry he didn't want to kill Bahry in Azkaban. In fact, that would have shortened that particular discussion considerably, in a situation where time was essential.
It has already been established that ventriloquism and silencing charms exist and that Quirell can do silent and wandless spell casting, so the "two plus two" test could easily have been faked.

All of them, as this is the first time Q hasn't turned into his Snake form first...

What could Harry use to get out of this pickle?

• His mind, obviously, especially since negotiation is a possible action.
• Wandless magic? (Presumably learned from Bacon's diary.) Probably not anything requiring lots of magical power, but recall from the Azkaban arc that he could dispel his own magic almost effortlessly even back then. Now that he finds second-year spells easy, he just might be able to wandlessly manage that or other spells requiring very little magical power, such as Somnium, Innervate, and the TPC. Or possibly very small transfigurations (like a millionth of a gram of botulinium toxin), since he's had so much practice with that branch of magic.
• Anything he's already transfigured and is carrying with him. Sulphuric acid chips?
• His control over Dementors, which he doesn't need spells for.
• Ritual magic? He may not need a wand to perform a ritual.
• Possibly a backup wand / Time-Turner / other useful device?
• Mastery over his Cloak? He didn't give it to anyone as a possession.
• Mastery / ownership of other objects? Perhaps the Philosopher's Stone also has an "owner" property?
• Summoning a phoenix? Even if he can't get a phoenix of his own, he may be able to call one to aid him in a selfless act of heroism.
• Plans (for help or otherwise) already set in motion? Someone might look for him at the Quidditch game (probably as part of the debate about the Snitch), realize that he's not there despite setting up the banner and being interested in the outcome of the debate, and go look for him. Or maybe he's hidden someone in his pouch, or told Cedric about what he's doing. Or due to the Bayesian Conspiracy, Draco will realize that he's been Obliviated and help Harry.

I've probably missed something, so feel free to add more in the replies.

Professor Quirrell then turned back to where the Potions Master lay sprawled, bent over and placed his wand on Professor Snape's forehead. "Alienis nervus mobile lignum."

The Defense Professor stepped back, and began to move his left fingers in the air as though manipulating a puppet on strings.

Professor Snape pushed himself up from the ground by smooth motions, and stood once more before the corridor door.

From Chapter 88: Time Pressure, Part 1, before anyone knows about the troll yet:

"You know," Harry said, as he turned his head away to stare at the ceiling illusion of a clear blue sky, "that still creeps me out sometimes."

"What does?" said Fred or George.

The powerful and enigmatic Defense Professor was 'resting' or whatever-the-heck-was-wrong-with-him, his hands making fumbling, hesitant grabs at a chicken-leg that seemed to be eluding him on the plate.

Are there any other times that Quirrell is described making similar gestures? (Note that another time he apparently controls someone else--the centaur in Chapter 101--he doesn't do this, but that may be due to the centaur actually being dead as some have speculated.) [Edit for Ch. 106: Confirmed; the centaur and Fluffy became Infieri.]

That still doesn't explain why he needs Harry to cooperate in obtaining the Stone. Even if it's more convenient to have Harry walking along, rather than towing his stunned body, Quirrel went to a lot of trouble to secure Harry's explicit help. He actually bargained and traded promises with him.

Which also leads me to ask: why couldn't Quirrel just make Sprout or Snape mind-control Harry using Imperius? Why did he have to bargain with him?

I originally interpreted the following as subtly implying the students were using prediction markets

A sudden air of attentiveness, as of long-standing disputes about to be settled. "Well, finally," someone said, as Millicent tried to catch her breath. "He's only got, what, ten days left to go bad?"

"Eleven days," said the seventh-year who was running the betting pool.

But it seems more likely that eleven days is how long the year has left.

I don't think there's actually any need even to rot13 it. This thread is full of spoilers and always will be.

The lowest grade is "Troll". Giving someone who was killed by a troll that grade would be in very bad taste.

Not a spoiler, but rot13'd for explaining the joke:

"All of you in this room... have received grades of at least Acceptable. Neville Longbottom... who took this test in the Longbottom home... received a grade of Outstanding. But the other student who is not here... has had a Dreadful grade entered on her record... for failing the only important test... that was given her this year. I would have marked her even lower... but that would have been in poor taste."

Gur bayl tenqr ybjre guna Qernqshy vf "Gebyy".

¡He terminado!