Tom at MusicThing scooped CDM on the Japanese cat costume accessory for your Big Briar/Moog theremin, but I'm surprised he didn't point out the other oddities at the same site, like a Matrioshka (Russian nesting doll) theremin shell.

You know, given nearly-unlimited choices of things to wave my hands
over, I just can't think of anything more appropriate than the
Matrioshka dolls. It reminds me of my childhood in Leningrad . . . ah,
as the theremin sounds floated through the streets . . .

That's it. I think we've now entirely exhausted peculiar theremin accessories. (But can we really be sure?)