Ok since everyone is on the topic of the ani-obi- duel i figured id throw in my 10 cents.
noticed that in this picture obi-wan has a lightsaber and anakin dont then in the far bottom right cornor you see obi-wans saber on the ground which means he some how has anakins saber. then I believe at some point anakin gets the choke on Obi-wan as in the trailer
Then in this scene we see Anakin chokeing Obi-wan but notice anakins saber is in obi-wans hand which kinda shows that in some point in the duel obi-wan loses his saber.
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Then notice in this scene Obi-wan has his own saber again which means that while anakin is chokeing him he drops anakins saber and then see's his saber and grabs his own and activates it.