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: Shares of GrubHub (NYSE:GRUB) sank on Wednesday after the company reported mixed first-quarter earnings. At 2:30 Wednesday afternoon, the stock was down 9.5% from the previous close.

So what: GrubHub reported robust year-over-year revenue growth of 50.5%, with its $88.2 million of quarterly revenue beating analyst estimates by about $3 million. Active diners rose 46% year-over-year, and gross food sales jumped 36%.

EPS doubled year-over-year, coming in at $0.12, but analysts were expecting EPS of $0.14. Guidance for the second quarter calls for revenue between $83.5 million and $85.5 million, with full-year revenue expected to be between $346 million and $361 million.

Now what: The decline in the stock price seems solely due to the company's earnings miss, but analysts may have simply been overly optimistic. GrubHub's operating margin jumped from 14% during the first quarter of 2014 to nearly 21% during the first quarter of 2015, with operating income rising by 125% year-over-year, far faster than revenue.

The drop in GrubHub's stock price seems like a major overreaction. There's almost nothing bad to say about GrubHub's quarter, except that earnings missed analyst estimates.