This has happened a couple of times to Frankie, totally freaked me out but as luck would have it the first time he did it we were waiting at baby clinic to get weighed so the HV was on hand to ask about it. She said it is quite common when they are teething as they produce a lot of mucus and saliva and it as many babies just swallow it, it ends up coming out in their poo. It can also be a sign of a tummy upset. Is he showing signs of teething or upset tummy?