Gary and Angela Williams of Northwest England were on a leisurely beach stroll when a pungent rotting-fish smell drew them to a lump of ambergris about the size of an American football.

The couple had read about the waxy excretion formed in the digestion system of sperm whales and often referred to as whale vomit. They knew the substance often used in perfume-making is rare and valuable, and wrapped it in a scarf and took it home.

"It was down a section of the beach where no one really walks," Gary told the Mirror. "It smells too bad, though. It's a very distinctive smell, like a cross between squid and farmyard manure."

It feels like a rock hard rubber ball. Its texture is like wax, like a candle. When you touch it you get wax sticking to your fingers."

"If it is worth a lot of money, it will go a long way towards buying us a static caravan [mobile home]. It would be a dream come true."

The Williams' are now negotiating with a buyer and hoping to make around $70,000.

It's thought that sperm whales secrete the substance in their intestines to protect the whale from the sharp, indigestible beaks of giant squid they frequently feed on. The whales eventually expel the ambergris from their mouths and that's why it's often referred to as whale vomit. The lumps can float for years and those pieces that don't break into little pieces sometimes land on beaches.

Even though harvesting ambergris doesn't require killing whales, many countries have banned the trade; the U.S. Endangered Species Act, for example, prohibits the possession and sale of it. But in the U.K. it's legal, and the Williams are allegedly negotiating with buyers in France and New Zealand, according to the Mirror.