I noticed that every time DS eats bananas, his stool contains black thread-like substance. I freaked out the first time I saw it. My pediatrician was not helpful or sympathetic at all so we switched. Luckily we have lots of doctor friends who told me not to worry but none of them can pinpoint what's causing this. I'm guessing it's the bananas. Anyone have the same situation? Is this common? Oh, DS happened to be sick the two times I found the black substance in his stool. First time, he had diarrhea. Thank you.