Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What's happening: Shares of Rosetta Stone Inc. (NYSE:RST) were up 20.5% as of 10:30 a.m. Friday after the language software specialist announced it has received an "expression of interest" from RDG Capital Fund Management.

Why it's happening: Whether RDG intends to make an acquisition offer or open a significant stake remains unclear, as Rosetta Stone didn't provide specifics on the communication. But Rosetta Stone's board did state "it will carefully evaluate the expression of interest," which comes as no surprise considering shares are still down around 23% so far in 2015 following a weaker-than-expected start to the year.

At the same time, the board noted it's still "actively implementing" the strategic plan it outlined in tandem with the company's quarterly report in March. That plan aimed to reorganize the business and lower its cost structure, which in turn should allow it to more effectively capitalize on its global Enterprise & Education (E&E) business. According to then-CEO Steve Swad, the E&E segment is where the company expects "to see the most profitable long-term growth potential."

That said, Rosetta Stone is simultaneously searching for a new CEO, as Swad later resigned as CEO effective April 1, 2015. In the meantime, Rosetta Stone director John Hass is serving as interim CEO. In any case, the expression of interest from an activist investor is an encouraging sign for loss-weary Rosetta Stone investors, and I can't blame the market for bidding up the stock so aggressively today.