I finally found the receipt from when I bought the plant - it's a Chinese Five Colour Pepper. The peppers that were once purple and woody have progressed to green, then yellow, orange and finally red.
I tried one of the red ones. My head instantly BURST INTO FLAMES. A pot of yogurt later and the feeling is just starting to come back to my nose. There's a painful red patch on my hand from where I spilled some of the juice.
Whoaa, mama.
That would explain why the squirrels haven't gone anywhere near them. I should plant a ring of them around the house, it would probably keep the mice out.
[ETA] Christ, I absent-mindedly put the back of my hand in my mouth to relieve the sting. Now my lips are on fire again. Shit on toast.