Audio problem: When Anakin says, "What? Uh-oh," his mouth does not move. He just looks shocked that his lightsaber could not cut The Zillo Beast.
Audio problem: In the Swedish release, the language suddenly switches to Danish, then back to Swedish again. This is according to the DVD copy I have of Season 4 Volume 1. (00:08:41)
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.