After Mace Windu decapitated Jango Fett, he looks somewhat surprised. Why? Was it because it almost looks like there was no body under that suit of armor?
Boba Fett and Count Dooku also look surprised. Boba is surprised because he just saw his father killed, but why Dooku? Is he worried that his "bodyguard" is now dead?
R.A. Salvatore's novelization did NOT mention any surprise:
And then it happened, all of a sudden. Mace started to slash to the left, cut it short and stabbed straight out, then reversed his grip and sent the lightsaber slashing across, left to right. He spun a complete circuit, coming around to parry a blaster shot, but there was no shot forthcoming.
That left to right reversal had cleanly landed. Jango Fett's head flew free of his shoulders and fell out of his helmet, to settle in the dirt.
Neither does the screenplay:
Finally, FETT isfree and kills the REEK. MACE WINDU fights fiercely with JANGO FETT. Finally, the bounty hunter falls. His helmet goes flying. The bounty hunter's body falls to the ground.
As far as the movie, it's not surprise on Master Windu's face, I think, but sadness (I'll try to see a formal explanation for it in Shatterpoint novel later):
Also, Dooku is merely looking unhappy, not surprised:
Master Windu's mood is explained in Matthew Stover's C-canon novel Shatterpoint, which centers on that character's story. He felt in the Force that what he must have done was to kill Dooku. Instead, he did not, and that permitted the Clone Wars to start, with no second chance to stop it. He's not sad at Jango's death, but at what that death means as far as signaling his failure.
In my dreams... My blade doesn't light the underside of Fett's square jaw. I don't waste time with words. I don't hesitate.
I believe.
In my dreams, the purple flare of my blade sizzles the gray hairs of Dooku's beard, and in the critical semisecond it takes Jango Fett to aim and fire, I twitch that blade and take Dooku with me into death.
And save the galaxy from civil war.
I could have done it.
Leaving that aside, there's is reason for many (any non-Jedi) to be surprised:
Windu himself has a healthy appreciation of Jango's deadliness. From Shatterpoint again, here's Master Windu's thoughts about Geonosian arena (from after the fact remembrance):
Jango Fett bristles with weapons. An instinctive killer: the deadliest man in the galaxy. Jango can kill me in less than a second. I know it. Even if I had never seen Kenobi's report from Kamino, I can feel the violence Jango radiates: in the Force, a pulsar of death.
We see that less that 5 minutes prior, Jango Fett easily killed another Jedi (A Jedi Master, and a member of Jedi Council to boot - Coleman Trebor) with his blaster, one on one. Here's the youtube clip of the event, and a small image montage I made from my copy of AotC:
We know that Windu uses a fight form based on his emotions (Form VII). He fights in a kind of trance, like a Sith, but he controls this trance. Maybe he doesn't really understand the reality of what he's doing during this trance until after his fight with Jango Fett. Fett, the best bounty hunter of the galaxy, is surprisingly not so good in his duels against Kenobi and Windu.
Windu wakes up from his trance like state, to see what he really did and feels remorse or is surprised at what he has done.
I think that Dooku is just disgusted, maybe stressed and fearful (a fearful Sith!).
I really agree (not the clone Gree, the verb) with the explanation of Shatterpoint. I have one other thing to say, sorry for my English, I'm French.
Windu is a Jedi. If you look into it, you'll find out that Jango was gonna try and fly away. But the rhino busted his jetpack, so that was impossible. Mace thought he was going to fly away as well, and was most likely going for his legs or jetpack thrusters.
There's also a chance in the heat of combat, he didn't notice destroying Jango's blaster -yes, it happens- and was attempting to deflect another laser blast.
In short, Windu was only trying to SUBDUE Jango, not kill him. Killing someone in front of their kid sure as hell isn't the jedi way. Windu's facial reaction is surprise from the fact that he ended up beheading Jango instead of subdueing him, and regret from the fact that he did it in front of his son.
It's a theory, but I think it's pretty well educated. Either way, that's my answer.
I am thinking Mace did feel guilty for having to kill Jango, rather than capture him. It might have even been respect.
As for Dooku, even though the game Bounty Hunter and the comics are just Legends now, and not considered canon, I think Dooku had respect himself for Jango and maybe some liking toward him, knowing that he wanted the first clone to be his son. He recruited Jango for the clones after all.
I think that Dooku is not surprised, but perhaps just astounded or maybe confused with how quick the kill was. Mace Windu is likely not surprised at all. He uses Vaapad, which is basically just aggressiveness through the lightsaber, not the mind, so he was probably just realizing that he killed Jango Fett, and in front of his eleven year old son. I highly agree with Shatterpoint, about him being in a trance of killing Dooku instead of the bounty hunter.
Judging from the look on his face, Mace seems to be relieved rather than surprised. Dooku on the other hand, did seem a bit surprised, but I always understood it as surprise for Mace Windu's aggressiveness. He kills as without hesitation, like a Sith, but without using anger and hate. This also surprises Dooku when he fights Anakin in their last battle.
Jango only had 1 gun w/ him. He also couldn't use his jet pack and was trampled by the rhino. Then when he fights windu he is kinda screwed. anyways I think dooku is just suprised he killed jango and so is mace
