Memento Mori

"I've got an app for that!"
Jermander looked over at Nicky, who was supposed to be doing their Poisons homework.  He harboured a slightly guilty hope that she would accidentally absorb some of the poisons that they worked with so that he could hang around with the cooler kids at Gorillamumps without his mum getting upset, but despite her natural klutziness, her trouble with the curvy letters of the alphabet, and her obsession with Harry Plotless films she seemed to be able to avoid poisoning herself.
"Got an app for what?" he asked, hating himself for talking to her when he was supposed to be solving horror-dimensional equations with pan-Lovecraftian coefficients.
"The book-thingy, here, says that this is a Memento Mori, and I've got an app for that already!  I don't need to make this poison!"  Nicky looked thrilled with herself.  She was an undine, a creature made of water, and when she was happy like this she threw off rainbows in random directions.  Jermander, a vampire, was not terribly keen on them as they burned his skin a little if they hit him.  He pulled his cloak around himself and regretted, not for the first time, that bats were incapable of directed thought about higher mathematics.
"A Memento Mori is a reminder of the transiency of life," he said, shuddering slightly as memories of his childhood came back to him.  "Father was very keen that we understood that when we were growing up, he always said that being creatures of unlife we needed to know what effect we would have on the lesser classes.  Well, actually, he always called them scum, but that's a bit de trop these days.  So anyway, whenever one of the estate workers died, whether they were shot in the back by some idiot who can't tell the difference between a grouse in the air and a man on the ground, or fell into the combine harvester when Father was playing jokes on people, or just caught a bad chill one winter which turned into galloping pneumonia and drowned them in their sleep, their bodies would be brought up to our house for a three-day vigil.  Which meant, really, that we'd have this dead body on the kitchen table for three days."
"How horrible!" said Nicky, her mouth hanging open and dripping slightly.  "How did you eat?"
"We just piled the bigger dishes on the body, and tucked the rest around," said Jermander.  "Except for the combine harvester guy.  We think he got quite a bit eaten actually, so we stuck some chicken carcasses in the coffin with him."
"Oh wow," said Nicky.  "I don't think I could eat a Memento Mori.  I'd chip my teeth."
"You've got teeth?"  Jermander's eyebrows disappeared into his hairline with surprise.  "I thought you filtered krill or something?"
"I have teeth for special occasions," said Nicky brightly.  "They're shiny!  But I'd definitely chip them on this app.  It runs on my phone, you know?"
"Let's see?"
Nicky passes her phone, a slightly corroded black smartphone with a scratched glass touchscreen and little colourful stickers on the back.  Jermander peered at it, and tapped hestitantly at the screen, eventually finding the right icon and bringing it to life.  It purred happily, a bell dinged and donged, and then the screen filled up with information.
"Oh right," he said, reading quickly.  "This is just a death-clock, Nicky, not a Memento Mori. It tells you when you can expect to die, based on your online data."
"When are you going to die then?"
"I'm already dead," said Jermander.  "I'm a vampire.  This thing expects me to have stopped trending on Twitter by the end of February, and to be... oh!  Staked through the heart, apparently, by the end of the century.  That's a tad brutal!"
"It says I've died three times already," said Nicky in a small voice.  "It said that voided the warranty."
"You're not dead though."
"That's what I keep trying to tell it!"
There was an awkward pose, broken finally by Jermander.
"The poison can't be a death-watch though.  Where's the text book?"  Nicky pushed it over, glad to be away from it.
"Oh right, this potion is just intended to force you to relieve parts of your life again, until you've moved on from it.  It doesn't actually kill you, but it looks like it'll hurt a lot."
"What should I do with it then, Jer?"
"Drink it?" suggested Jermander sitting down and sighing as he looked at his paper.  The Lovecraftian variables were writhing around and trying to hide.