What happened

Even as market indexes turned lower Wednesday, not all stocks were feeling the pinch. Both the S&P 500 and the Nasdaq Composite were sharply lower, down 1% and 1.5% (as of this writing around 12:30 p.m., ET).

Bucking the trend however, were these three stocks that appear to have nothing in common, at least at first glance. Clinical stage biotechnology company Cassava Sciences (SAVA 4.93%) surged as much as 72.5%, meal kit purveyor Blue Apron Holdings (APRN) climbed as much as 27.1%, and cosmetics company Revlon (REV) gained as much as 15.2%.

At 12:45 p.m. ET, the stocks' move from the previous close were 28% for Cassava Sciences, 10% for Blue Apron, and 1% for Revlon.

My quick check of usual sources found very little in the way of company-specific news fueling the gains. However, I found a common thread that might have helped drive the threesome higher. Interestingly, it's that many investors are betting against the stocks.

So what

There are a number of ways to make money from the stock market. The most commonly employed method is buying stocks in companies with long-term opportunities and holding them as the stock price goes up.

Shorting a stock is a strategy used when investors believe a stock will decline in value. In this process, investors borrow shares of the stock from a broker and turn around and sell those shares to other investors, pocketing the proceeds. They are still on the hook to return the borrowed shares to the broker.

So they eventually have to buy shares back so they can return them. They are betting the stock price will drop so that they can buy them back for less than they sold them for.

Things can go awry for short investors if the stock price goes up and they are forced to buy the shares at that higher price. 

If a heavily shorted stock experiences a rapid price increase, short-sellers can be pressed into buying back shares quickly in order to minimize their losses. If a large number of investors have shorted a stock and the price jumps, this can result in a short squeeze. As the stock price rises, shorts scramble to replace the borrowed shares, increasing demand for the stock and sending the price rocketing even higher.

Now what

A quick look behind the scenes suggests that this could be the catalyst that drove this trio of stocks higher today.

At Cassava Sciences, a full 30% of the float -- or the total shares available to public investors -- was sold short as of July 29, according to Yahoo! Finance. That amounts to nearly 29% of the company's outstanding share count. At Blue Apron we find 23% of the float sold short, amounting to 29% of the company's outstanding share count. Rounding out our trio, Revlon has 35% of the float sold short, amounting to 5% of the company's total outstanding share count.

Further evidence that the shorts are perhaps driving today's move can be found by comparing the current trading volume to the three-month average for these stocks. In the case of Cassava Sciences, more than 23 million shares traded had hands as of around noon on Wednesday, more than 15 times its average daily volume over the past three months. Blue Apron saw more than 11 million shares traded, nearly four times its three-month average.

For Revlon, however, nearly 4 million shares changed hands Wednesday, below its recent three-month average of more than 19 million shares. But since Revlon stock has recently joined the meme stock movement, shares have been part of an epic and ongoing short squeeze, with the stock up more than 650% since mid-June.

This helps to illustrate that potential hazards of shorting a stock. It's also wise to remember that a short squeeze can be short-lived. As of 12:31 p.m. ET, Cassava Sciences had given back more than half its gains, up 30.6%, while Blue Apron and Revlon were back closer to breakeven, up 2.8% and 0.2%, respectively.