Metamorphoses
Achelous and Hercules fight for the same girl, Deianira. At first Achelous evades Hercules by transforming into a slippery snake, but Hercules eventually tears off his horn and defeats him.
The centaur Nessus also loved Deianira. Nessus offers to help Hercules and Deianira cross a stream, but when Hercules thinks Nessus is kidnapping Deianira, he kills Nessus. In return, Nessus “gave / his shirt soaked in warm gore to Deianira, / a talisman, he said, to kindle love” (203). Later, when Deianira is insecure about Hercules’ loving another woman named Iole, she gives him the shirt, poisoning him with the centaur’s blood.