Continuity mistake: The Resolute's bridges are missing their red colouration when it arrives at Ryloth and moves to angle its hull towards the Separatist ships. (00:20:51)
Continuity mistake: When Obi-Wan, Waxer and Boil take cover behind some rocks on the way in to Nabat, in a close-up of Obi-Wan, the armour markings of the trooper next to him are missing. (00:04:37)
Continuity mistake: Obi-Wan drops his lightsaber during the run-in with the gutkurrs, and Cody is explicitly shown returning it to him after the creatures are contained. However, when Obi-Wan initially releases his control on the creatures, the weapon is visible on his belt. (00:17:24)
Continuity mistake: When Obi-Wan lines up his commandeered cannon for a second shot and Waxer and Boil load in another charge, they grab the ammunition from the same exact position at the top of a stack that they took the first ammunition charge, used for Obi-Wan's first shot with the commandeered gun. (00:21:09)
Continuity mistake: When Commander Ponds is first seen, running between the AT-TEs travelling along the canyon wall, his kama (kilt) is missing in the second shot of him before reappearing in the next one. (00:01:22)
Other mistake: When Cad Bane orders one of the commando droids disguised as a Senate Commando to finish clearing the platform, the neck area below the helmet shows human skin even though there's now a droid inside the armour. (00:02:07)
Answer: Dooku never accepted Ventress as his apprentice, as far as I know; he just kept her as his devoted personal assassin. In Phantom Menace, it is stated that there can be only two Sith at a time, to prevent a power struggle in the lower ranks. To accept Ventress as an apprentice, Dooku would have violated that rule.