okay everyone buckle the hell up cause I'm gonna nerd out to you about the makeup they used for this episode.
Yeah that's right I SAID MAKE UP
Everything from the top of their head to the end of their neck
purely intricate, beautiful makeup
(by the very talented make up designer Sheelagh Wells who is the only one to have worked both on doctor who in '63 and new who)
Each shaped individually to each actors face and able to pick up each micro expression we still struggle to produce with cgi to this day without it looking wrong or plastic
everything from the small cheek movements to the eyebrows to the nose crinkle, the actresses is able to act as if she usually would.
By not having to restrain her face to act in one peticular spot or with nothing but small motion capture dots on her face, means she can actually bounce off the more realistic reaction to the other actors performance rather than if they just said "right well pretend she's a cat and we'll add it in later".
and sure, okay, I'm not gonna lie to you, the main reason the nun cats were made to be nuns was because it meant that they could cover up as much skin as they possibly could to save time in the makeup chair, because like op said, they truly did have the budget of a crisp packet
Yes, each actresses sat in the makeup chair getting the extensive hair and make up done for HOURS, but ultimately the sheer amount of detail they were able to add to the characters by doing this made it worth their while.
THEY ONLY HAD A BUDGET OF AROUND £800K PER EPISODE at the time, in 2006 FOR EVERYTHING INCLUDING LOCATION ETC
Imagine what these make up designers would be able to do with A HOLLYWOOD MOVIE BUDGET