Complex sentence: The pickled body was removed and, upon inspection, it was discovered that the sailors had drilled a hole in the bottom of the cask and drunk all the rum, hence the term "Nelson's blood" being used to describe rum.
Split into simpler sentences: The pickled body was removed and, upon inspection, it was discovered that the sailors had drilled a hole in the bottom of the cask and drunk all the rum, in the process drinking Nelson's blood. Thus, this tale serves as a basis for the term "Nelson's blood" being used to describe rum.