Below the Lucasfilm announcement there is a short message by Dave Filoni and then a clip of an episode next season. In the clip, Anakin and two other Jedi females are fighting in a battlefield somewhere indoors. The clones are all looking very Episode III-y now. Anyway, one of the clones is feeling a little lightheaded, and then he says something like "A soldier must follow orders," and marches towards a Jedi. He points his gun at her, and fires.
This isn't the first time we've seen clones killing Jedi, but this wasn't Order 66. Right after the clone killed the Jedi, the commander ran over and tackled him down. Anakin said that he "wanted answers" to why the clone killed the Jedi. Another notable item was that several droidekas/destroyer droids appeared along with several red Super Battle Droids who are sporting jetpacks.
At the end of the clip, it turns out the whole battle is being surveyed by... Admiral Trench. No, you did not hear wrong, it is the same spider-like Admiral Trench that was killed in "Cat and Mouse", and another time before that, according to Admiral Yularen. However, this time it does look like he hasn't escaped the torpedo that destroyed his ship without a few scratches. One of his eyes is robotic. He strokes his chin and replays a hologram clip of the clone killing the Jedi. Then he tells his tactical droid something like "Call Count Dooku, I found something interesting."
There are several possibilities for this clip. It may have been some Separatist plot that Trench didn't know about, it might have been the Nightsisters (not very likely) or, an interesting theory that I came up with: the clone was feeling ill, and he somehow thought that Order 66 was happening. Then the clones would be nervous because they wouldn't want to reveal that Order 66 even existed.