Thursday saw what experts are calling the largest inter-day drop in the Dow Jones's history. Although it appeared to be triggered by unrest in Greece, the real cause could be a trader's "fat fingers."

As demonstrators filled the streets of Athens Thursday, the North American markets opened, and immediately started dropping.

"There was a building concern, not only in the stock market, but also in the currency markets and credit markets, that the problems we have focused on Greece were not being contained," Vancouver trader Victor Adair told CTV News.

And when Greek lawmakers approved a 110-billion-euro bailout package, the Dow Jones industrial average plunged 1,000 points.

"There was panic in the market today," Adair said. "You have to think that there's something going on in the market that I don't know about yet, and I can't wait to find out what it is."

The TSX started falling -- dropping more than 450 points –- and the Canadian dollar fell by about two cents.

"It's what we used to call in the brokerage business a ‘G.M.O.' order. That's ‘Get Me Out,'" Adair said.

But just minutes after the free fall began it was over. The Dow rebounded, closing down a slightly less alarming 342.88 points. The TSX only lost 32.7 points on the day.

And unbelievably, evidence began to emerge that the record drop in the market was a result of a trading error -- specifically what's called a "fat finger problem."

A trader at a major Wall Street investment bank reportedly entered a "b" for billion rather than "m" for million on a trading form.

But Adair believes the temporary crash and panic was a sign of a jittery market.

"There's something going on and this error just hit the market. It was like an accident waiting to happen, and it happened," he said.

His advice to investors is to keep an eye on the situation in Greece. Today might have been an error, but what's happening in Europe is very real.

With a report from CTV British Columbia's Shannon Paterson