Mystery poop on the floor.

[Stacer]

Today we discovered a poop outside the litterbox. This has never happened in the nearly 4 years we've had Angus and Finn.

What can cause a cat to poop outside the litterbox?

The poop looked normal in every way. We regularly scoop it. We haven't changed litter brands in a while (but that never seems to bother them anyway). They've always shared 1 box without incident (I know, I know, 1 for every cat plus 1). Food is the same, their behaviour is the same. Nothing at all is out of the ordinary except for this poop on the floor beside the box (no idea which one did it).

Any ideas?