I got one of those not long ago. One of my silkies laid one smaller than the quail eggs.
The 2 in the back are what size it should have been and the 2 spotted ones are the quail eggs.
I have on Araucana and it always has laid tiny eggs since it's a real tiny girl - but sometimes it just comes up with these absurdly small things. I can fit four into a single-egg chamber of a box.
But yours is still smaller... and round!
(or am I losing my mind and fart is some sort of nickname for a chicken?)
But dude... 'egg farts' are totally what these should be called if they're not. Because she sure as hell didn't LAY an egg.
I get fart eggs from the quail every now and again and you want to talk about a small egg. These are tiny. I'll have to take a pic next time I get one.