The market erupted today to end on record highs, as the S&P 500 (SNPINDEX:^GSPC) finished off a great day by surging for a gain of 0.6%, or more than 12 points. Europe kicked things off with an aggressive move by the ECB to pressure banks into lending money in an effort to combat floundering inflation, and Wall Street celebrated, as stocks kept up the momentum from there. Not every pick on the market did so well today, however: Smith & Nephew (NYSE:SNN), Rite Aid (NYSE:RAD), and Zynga (NASDAQ:ZNGA) spent the day mired in the red, and disappointing investors. Let's check up on today's three worst stocks.

Is Smith & Nephew the next acquisition candidate?
Smith & Nephew's stock has had an eventful past month. With takeover rumors abounding around the medical-device industry, this company's been squarely in the crosshairs of analysts considering the next possible acquisition candidate. Orthopedics leader Stryker has already been linked to Smith & Nephew, and today, Wall Street crowded around rumors that Medtronic (NYSE:MDT), the market's largest pure medical-device player, was interested in bidding for this company.

So why the 5.7% drop-off in Smith & Nephew's stock? Medtronic downplayed its interest in Smith & Nephew by refusing to comment on the speculation. The company is also looking to return overseas cash to shareholders without undergoing a tax inversion to incorporate outside of the U.S., something that initially sparked the rumors of a bid for the U.K.-based Smith & Nephew. Still, while Medtronic may not be as serious a bidder as hoped for, the wave of consolidation in the health-care sector means that investors likely haven't seen the last of Smith & Nephew branded as a takeover candidate.

Rite Aid in Boise, Idaho. Source: Wikimedia Commons

Rite Aid took a heftier blow today, plunging by more than 7.4%, although the stock mounted a minor comeback in early after-hours trading. The culprit behind the drop? The company slightly lowered its fiscal 2015 full-year earnings estimates, and projected first-quarter earnings of only $0.04 per share for the current quarter, half of what analysts polled by Reuters expect on average. While the news hurt, this stock probably took a plunge partly behind profit-taking on the strong year-to-date gains of the shares.

Rite Aid has still done a good job keeping its top line growing despite the hit from generic drug competition that the company reported today. The firm's same-store sales growth came in at 3.5% for last month, below rival Walgreen's reported 4.4% same-store growth for the month, but nonetheless a respectable figure. Rite Aid's stock is still pricey on a price-to-earnings valuation basis as compared to Walgreen, but given this stock's colossal run-up since 2014 began, today was more of a step back from the year's rise more than a drastic disappointment.

In the tech sphere, Zynga took one of the biggest blows on the market today with a 9.2% plummet. This stock has been anything but good for investors during the past three months, nosediving by more than 42% in that time. Three more executives left the company today as reported by VentureBeat; these are the latest departures in CEO Don Mattrick's makeover of the firm's leadership. While Mattrick pushed out old leaders in order to reform the company under his goals, Zynga has continued to see revenue and earnings dive. In its most recent quarter, the social gaming company's sales plunged by 36% year over year. While Zynga recently has attempted to ease the pain through workforce reduction and acquisitions, the company's user base and financials tell a story of a firm that's struggling to hang on to investor confidence. Until Zynga can show marked improvement, don't expect a serious turnaround from this stock.