A perfectly preserved severed dead cats head.
In a plant pot that had had thyme in it, which I'd been picking and using for ages.
Outs self totally to anyone who knows me/has done a training course with an ice breaker thing with me 
I was happily repotting my lovingly tended herbs and... dead cats head.
I can still see it. Small, grey, perfectly formed, fur intact. I'm my plant pot.
It was 20 (ekk) years ago and my two flat mates were out. I remember it was a lovely summer day and I had the day off work.
I screamed and ran about ineffectually for a bit then put an empty plant pot over it.
It was a very hot day, I ran inside and hyperventilated for a bit then went back outside. Flies had gathered.
So I did what any sensible person would do, cracked open the wine (it was about 11am), downed 2 large glasses in quick succession, ran out and put the whole lot into 2 massive bin bags, ran through the house and put them in the bin at the front.
The combination of perfect cat head preservation and eating the thyme finished me.
With time and more wine we worked out that what had probably,no it was definitely a strange voodoo ritual by persons unknown to kill us all to death happened was that the previous winter me and my greenfingered housemate had dug over the garden and used some of the soil to pot up herbs/bulbs.
So we unearthed a pagan burial ground/sacrificial offeringand unleashed a curse on our houses until the end of time probably dug up the previous owners much loved pet.
Still, fair ruined my day off.