I am so sorry to have missed this yesterday! I am glad to hear Fister seems to be doing ok now. It does sound to me like a bit of constipation, and when you describe the poop as hard on one end and soft on the other...well, that really sounds like it. He might strain so much to get the hard end out, then the rest follows as it normally would. I think maybe it is an anal fissure of some type. But, do call the vet, as I know you will.

Little kisses to my boy, Fister!