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

A sell-off in emerging markets appears to be setting the tone for developed markets on Friday, as U.S. stocks opened lower, with the S&P 500 and the narrower Dow Jones Industrial Average (DJINDICES:^DJI) down 0.69% and down 0.61%, respectively, at 10:15 a.m. EST.

One predator that has found a prey will often attract another.

Juniper Networks (NYSE:JNPR) was the third-best performing stock in the S&P 500 last week and it looks likely to be one of the best performers again today, if this morning's price action holds -- the stock is up nearly 10% at 10:15 a.m. EST. Last week's performance followed the announcement by activist hedge fund Elliott Management that it owned 6.2% of the tech company's stock. The hedge fund also released a presentation detailing its "value plan" for Juniper, which it believes could raise the stock price to $35-$40 by cutting operating costs by $200 million and initiating a $3.5 billion capital return program.

Today's pop in the stock price is the result of news that another activist fund, Jana Partners, has sent a letter to its investors stating that it is now one of Juniper's largest shareholders and calling for similar actions to those outlined in Elliot's presentation. Jana thinks the company ought to cut $300 million in costs and implement a capital return program.

The activists are not going unheard. During Juniper's quarterly earnings call yesterday, CEO Shaygan Kheradpir, who only just took the reins of the company on Jan. 1, referred to himself as an "agent of change" and said that he would review its cost structure and consider share repurchases and dividends.

Juniper disclosed on Thursday that it has more than $4 billion in cash and equivalents; Elliott Management's presentation observed that, at nearly one-third, "Juniper's net cash balance as a % of market cap[italization] is among the highest in large-cap tech." Indeed, on that measure, Juniper outranked the cash-heavy triumvirate of Microsoft (25%), Cisco Systems (26%) and Apple (NASDAQ:AAPL) (27%). Need I mention that two among this trio, Microsoft and Apple, are themselves the objects of activist investors' efforts?

Indeed, Carl Icahn this week lamented on Twitter what he called the Apple board's "grave disservice to shareholders" in not having "markedly increased its buyback." However, with Apple having embarked on a multiyear, $100 billion capital return program, Icahn's cries ring hollow and his stake of less than 1% affords him limited influence. Juniper Networks, on the other hand, will be hard pressed to shake off Elliot Management and Jana Partners; expect some of its cash pile to begin flowing back to shareholders.

Fool contributor Alex Dumortier, CFA has no position in any stocks mentioned; you can follow him on Twitter @longrunreturns. The Motley Fool recommends Apple. The Motley Fool owns shares of Apple. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.