I love this. So visceral. It makes your tongue curl up as she looks for hers. With phrases such as "viscous liquid, starting at the back of her throat and making its way forwards, before trickling out of her lips, down her chin and onto her lap" you can see why you gave this piece the erotic tag. The sex is in the subtext and that's where it's most unsettling. Overlaid with this surreal violence and mystery it paints a very uncomfortable, extremely physical feeling. An imaginative way of going about things, original or at least not much seen outside of Chuck Palanhiuk and he's begging for a successor.
But the piece does raise a few questions. Why is this happening? Is it a metaphor for how one can say far too much for a delicate situation, such as a family meal on thanksgiving? Her tongue literally escapes her. But then why do the rest of her organs follow suit and why is this happening on thanksgiving? Horrific food poisoning? You're an English author and yet you've chosen to set this on an American holiday. Possibly you were trying to create a more Americanized feel to the piece or could it be a continuation of the whimsy you show in phrases like: "She checks under the cat"?
I love the idea that the narrator hears what she says personally, maybe he is actually there and completely inactive. It highlights an interesting issue as to why these involved yet distant narrators that often go nameless never actually help with the situation they recount. Could it be that they lose their ability to act in their attempts to record the moment?
But yeah, all in all, great piece. I love how vivid a situation you create in what is quite a short piece. I'll have to give some of your longer works a try when I have time.