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: Mentor Graphics Corp. (Nasdaq: MENT) popped 14% in intraday trading today after Carl Icahn offered to buy the company for $17 per share, a 17% premium to the stock’s closing price Friday. (The market was closed yesterday for Presidents Day.)

So what: Icahn is an activist investor known for, among other things, demanding management changes and/or taking companies private in order to restructure them and improve operating results. After he acquired a greater-than-5% stake in Mentor Graphics last year, the company put a poison pill in place.

Now what: Icahn’s offer is all cash and does not carry a breakup fee. This leaves plenty of opportunity for Icahn and other shareholders to profit from higher bids. Icahn doesn’t bat 1000; failures include investments in Yahoo! and an attempt to take over Dynegy that did not receive sufficient shareholder approval.

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Fool contributor Cindy Johnson does not own shares of any company named above. 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.