My mother had gone through piles operation in April 2017 .she had 2piles. 1 was removed and the other one is not removed because she has diabetes. She has black colour blood in her stool. She has soft stool .what is the reason of black colour blood? Also she feels like some hard tissue like in the operation site (inside anus). Is it possible that any plastic thread was left in the body? The operation was done at home. After operation she has more gas problem.