What's Inside Worcestershire Sauce?

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Though Worcestershire sauce was originally developed in India by the English, it takes its name from the fact that it was first bottled in Worcester, England, by two dispensing chemists, John Wheeley Lea and William Henry Perrins. It's a thin, dark, rather piquant sauce used to season meats, gravies, soups and vegetable juices, and as a table condiment.

You may know about the garlic, onions, anchovies, and vinegar but what else is inside Worcestershire sauce?