Guess how I found out...
actually, he was having a holy temper tantrum in his crate. Now, he has frewuent tantrums in his crate but this one was REALLY REALLY bad. After a few minutes I gave in and went to see what his malfunction was this time. Poor little guy was jammed against the door - to get away from what he had deposited at the other end of the crate.
I felt really bad
I threw in a chicken neck, liver and heart with each dog's meal tonight. I didn't think that small of an amount could have such an effect. Not that I was expecting an effect in the first place....