What was he thinking?

My apologies if this story grosses you out, but it has to be told. When I got up this morning, I noticed a pile of small rocks on the rug in our dining room. They were the kind of gravel-like stones that are in part of our backyard/garden. The area surrounding the rock pile looked suspicious as well. Kind of like how it looks if Grady has thrown up and then eaten it back up (why do dogs do that?). Sure enough, this afternoon while walking Grady I saw more evidence of rock-eating when I used my Basel Stadt-provided dog poop bags. When unchaperoned, Grady has been known to eat cat poop in our backyard. I'm not sure what's worse, rocks or cat poop. While I was watering the garden yesterday there were several minutes where Grady was not within my sight, and once I saw him again I noticed he was digging around in this very rocky part of the yard right near the driveway. My guess is that the neighborhood cats have been using the rocks as their litter box and Grady was having a feast. From his perspective, there was no time to discriminate against the rocks-- knowing it was only a matter of time before I caught him-- so he must have just eaten it all. Oh, the joys of having a lab.