When I first got my snake the same thing happened. It was stress. I got worried too and called a vet. He said it was more than likely stress. And when my snake started to trust me and realize I wasn't trying to kill him he was fine. I also think a feeder that has been thawed in water can soak up water and cause a more loose stool but that is just a guess because I started thawing mine by just laying it out for 3 to 4 hrs. rather than thawing in water I changed over because the water soaked ones seemed to cause wet stool in my opinion. But that was just my experience that happened a couple times. Might not have been due to the water. A couple times I sealed it up in a bag ( air tight ) and weighed it down. But ended up now just laying em out to thaw then using a heat lamp to finish.