Source text
وَبِانْتِفَاخِ حَيَوَانٍ وَلَوْ صَغِيرًا
• If an animal dies in the well and its carcass swells, decomposes, or begins to come apart, complete drainage is required even if the animal is small.
• The important point here is the decomposed or swollen state of the carcass.