Why does Movie-Quirrell not shake Harry's hand in the Leaky Cauldron?

Question

In the movie Harry Potter and the Philosopher's Stone Harry and Hagrid meet a number of people in the Leaky Cauldron during Harry's first visit there. Among them is Professor Quirrell.

Harry offers his hand in greeting, but Quirrell does not shake it, but instead folds both his hands.

The out-of-universe reason for this is obviously the fact that in the movie version he is already wearing his turban, is presumably therefore already possessed by Voldemort and if he could touch Harry without burning his hand, a continuity error would occur with the end of the movie, where the audience learns that Quirrell cannot touch Harry without burning himself.

In the book, the problem is avoided, since Voldemort possesses Quirrel after the latter's failure to aquire the Philosopher's Stone (the artifact) from Gringotts.

Movie-Quirrell is however as surprised as Book-Quirrell when at the climax of the movie, touching Harry burns his hands (and face): so why would Movie-Quirrell shy away from shaking the boy's hand in greeting, something literally the whole pub does (some more than once)?

I only see two possibilities:

1. he knows touching Harry will give the possession away, and avoids doing it in the Leaky Cauldron - and then stupidly attacks Harry at the climax of the movie with his bare hands instead of just using his wand (AK the kid and done), or
2. he doesn't know and therefore acts appropriately surprised at the climax - but why then does he not grasp Harry's hand (like Book-Quirrell does - as Slytherincess quotes in her similar but kind of opposite question about why Book-Quirrell doesn't get burned)?

Answer 1

Out of Universe: Foreshadowing

As NKCampbell and Valorum note in the comments, from the filmmakers' perspective, it's better to avoid the handshake than to include it (including it would create a plot hole difficult to explain in the movies).

Besides, it's a trick similar to the typical Rowling foreshadowing, where the clues are right there but don't make sense until the climax. This moment is portrayed as an example of Quirrell's (ab)normal twitchiness and nervousness. Much later in the movie, the audience realises that there's a real reason that Quirrell couldn't touch Harry.

In Universe: Quirrell's Fear

Quirrell was in the Leaky Cauldron that day for one purpose: to steal the Sorcerer's (Philosopher's) Stone. His mission had nothing to do with Harry. Now at this point, Harry Potter was an enigma in the Wizarding World (even to Voldemort himself). He was the famous wizard who defeated the Dark Lord at the age of one. There was no telling what powers he possessed; perhaps he was even a Dark wizard himself.

“Have you not understood me? It was only Dumbledore’s protection that was keeping me out of Azkaban! Do you disagree that murdering his favorite student might have turned him against me? But there was more to it than that. I should remind you that when Potter first arrived at Hogwarts there were still many stories circulating about him, rumors that he himself was a great Dark wizard, which was how he had survived the Dark Lord’s attack. Indeed, many of the Dark Lord’s old followers thought Potter might be a standard around which we could all rally once more. I was curious, I admit it, and not at all inclined to murder him the moment he set foot in the castle.

“Of course, it became apparent to me very quickly that he had no extraordinary talent at all. He has fought his way out of a number of tight corners by a simple combination of sheer luck and more talented friends. He is mediocre to the last degree, though as obnoxious and self-satisfied as was his father before him. I have done my utmost to have him thrown out of Hogwarts, where I believe he scarcely belongs, but kill him, or allow him to be killed in front of me? I would have been a fool to risk it with Dumbledore close at hand.”

_{(Spinner's End, The Half-Blood Prince)}

Now at this moment, Quirrell was the only one who knew that Voldemort was planning a comeback. He was genuinely terrified of being found out. Given that Harry Potter was such a mysterious and daunting figure (at first; this entire incident took place before the Wizarding World figured out that Harry "had no extraordinary talent at all") who had a specific grudge against Voldemort, Quirrell would understandably be startled at chancing upon him in the pub. His thought process would go something like "AVOID HARRY POTTER AT ALL COSTS". So he decided to keep as much distance from Harry (like avoiding physical contact) as possible without appearing suspicious (slipping out of the door the minute Harry walked in would raise even more suspicion than refusing to shake hands with him).

I know that this is a bit of a stretch, but then again, most in-universe movie explanations are.