Captain Rex Doesn't Talk To Separatist Scum

Asajj Ventress: Take care of what's left of the clones! I'll go after Skywalker! Battle Droid Commander: Roger! Roger! Asajj Ventress: Seal the main gate on all portals! Let no one escape this castle! Battle Droid Commander: Yes, Mistress! 
Asajj Ventress: Where is Skywalker? Captain Rex: I don't talk to Separatist scum!