This is a huge threat to the Dow

Some of the largest emerging market currencies have taken a hit in the last several months and, according to one highly respected follower of the markets, this will have serious repercussions for many large US businesses.

Since the start of May, many world currencies are down dramatically against the US dollar. In that time period, the Brazilian Real is down nearly 22% and the commodities-based Australian dollar is weaker by 13%. Meanwhile the world's second-most populous country,India, has seen the rupee devalue by 19%.

(Read: 'Bernanke Bubble' going bust in emergingmarkets)

Joe Weisenthal, Executive Editor of BusinessInsider, is on top of the finance like few else; the New York Times referred to his work as "one man's ruthless, relentless pursuit of market minutiae". In an interview with Talking Numbers, Weisenthal says there are three reasons emerging market currencies have gotten so volatile and he explains how it's going to hurt some of America's biggest businesses.

While the US is contemplating the Federal Reserve Bank tapering its $85 billion per month bond-buying operation, many countries are having a strong reaction to Fed policy, notes Weisenthal. Known as "quantitative easing", this policy boosted bond prices, thereby bringing bond yields to lows near-record lows in first half of the year.

(Read: Your guide to reading the new Fedminutes)

However,talk of tapering beginning in May led to a bond sell off and that raised interest rates in the US. This, in turn, made the American dollar more attractive relative to other currencies. Yet Weisenthal says there are other reasons why many currencies – particularly in emerging markets – have fallen so far so fast. And that is already starting to shake up a lot of big companies, including several Dow Jones Industrial Average components.

To hear why three reasons why currencies have gone wild and what that means for some of America's leading corporations,watch Weisenthal's Talking Numbers interview in the video above.