Why did Obi-Wan flinch during the battle with Darth Maul?

Question

After a brief staredown where the camera zooms in on Darth Maul and Qui-Gon's face, both Qui-Gon and Obi-Wan charge Darth Maul -- but not before Obi Wan looks like he just got pelted in the forehead and goes "Ugh!"

(this is right before Maul back-flips to a higher bridge)

_{Better illustrated in this video}

Perhaps Darth Maul did some weird Force thing off-screen, but it still seems very strange. What is happening here?

Answer 1

I always interpreted it as as feint rather than a flinch. Obi-Wan and Qui-Gon coordinated with each other to make the most out of their numerical advantage.

For reference, here's a .gif of the scene in question (taken from the video linked in the question):

Obi-Wan made an exaggerated motion with his head and lightsaber as if about to attack in order to distract Maul (and he grunted to add to the distraction). Maul was successfully distracted, and Qui-Gon was ready to attack. Maul, in turn, realized almost too late that the attack was coming from Qui-Gon instead of Obi-Wan, so he was forced to retreat by jumping back onto the pathway behind him.

Answer 2

• The Terry Brooks novelization does NOT offer any "flinching":

  Qui-Gon Jinn and Obi-Wan Kenobi stood alone in the Sith Lord’s path. Together, they removed their capes and ignited their lightsabers. Their horned antagonist stripped away his cloak as well, then lifted the long-handled lightsaber he bore as if offering it for inspection. Gleaming blade fire jutted from both ends of the handle, revealing a deadly, dual-blade weapon. A smile crossed the bearer’s feral face as he swung the weapon before him in an idle, casual gesture, beckoning the Jedi ahead.

  Spreading out to either side, Qui-Gon and Obi-Wan slowly advanced to meet him. ...

  Qui-Gon and Obi-Wan closed with the Sith Lord in a clash of lightsabers that produced the shriek of diamond-edged saw blades cutting through metal. ...

  I read the rest of the novelization and it mentions absolutely nothing about Obi-Wan flinching or similar, up till the time they get separated by the walls.

  Note that the freeze-frame in your question is right before they prepare to attack Maul but he jumps up from one bridge to another:

  They fought their way out of the main hangar through an entry that led into a power station. Catwalks and overhangs crisscrossed a pit in which a tandem of generators that served the starship complex was housed. The room was cavernous and filled with the noise of heavy machinery. Ambient light filtered away in clouds of steam and layers of shadows. The Jedi and the Sith Lord battled onto one of the catwalks suspended above the generators, and the metal frame rang with the thudding of their boots and the clash of their lightsabers.

  Alone in the power station, hidden from the rest of Theed and its occupants, they intensified their struggle.

  The Sith Lord leapt from the bridge on which they fought to the one above

• Wrede's Junior novelization doesn't exactly help too much, condensing the entire fight to:

  Obi-Wan had never been in such a lightsaber battle before. So this is a Sith Lord, he thought fleetingly as he dodged and leaped. It was taking every skill he knew just to stay alive. The Sith Lord seemed to cloud Obi-Wan’s use of the Force, making it hard to sense his opponent’s moves and counter them in time.

  Slowly, the Sith Lord forced Qui-Gon and Obi-Wan back. Out of the hangar and down a long hall they fought, then on into the Theed power generator plant. The Sith Lord leaped from one service catwalk to another, and the two Jedi followed. Qui-Gon was in the lead now, taking the brunt of the attacks. The narrow bridge gave them little room to maneuver. Obi-Wan tried to close in on their opponent, but the Sith Lord twisted and kicked him off the catwalk.

• I watched the DVD and found the moment the screenshot belongs to.

  I have frame-forwarded the film for the next few seconds.

  To me it looks like

  • He set up to attack with his blade

  • He noticed that Maul put up his right blade into blocking position

  • He shifted his stance and allowed Qui-Gon to strike first as he was less likely to be blocked.

  But that's just how it looks like.