While the market often turns on little more than a whim, it can also move with a hint of logic behind it. Today, Wall Street decided it was time to pull back a little after a six-week rally left the S&P 500 Index (SNPINDEX:^GSPC) at its highest valuation in about a year and a half. While the S&P fell less than 0.1%, its three biggest decliners fell a little more hastily.

As can frequently be the case, Western Union (NYSE:WU) fell on Monday, mostly for the simple reason that the company reports earnings tomorrow; a number of investors became anxious that the numbers wouldn't be in line with estimates. It could also be the case that investors forgot just how unimpressive Western Union's results are projected to be: Sales are expected to decline by 2.3% as EPS contract by a crushing 12.5%. Either way, the stock's 2.8% fall today was the steepest of all 500 S&P components. 

Natural gas company WPX Energy's (NYSE:WPX) 2.3% fall Monday was the result of a broader decline in the S&P 500's energy sector, which, declining 0.6% on the day, was just bad enough to be the worst performer in the 10 sectors. Also not insubstantial was the U.S. Energy Department's weekly report on natural gas inventory levels. While natural gas supplies did fall, they fell less than expected, meaning that natural gas prices may be even lower than projected. 

The third and last of today's decliners is the online streaming company Netflix (NASDAQ:NFLX), which dropped 1.7% Monday. Shares in Netflix have rallied by a remarkable 123% in the past three months alone, with most of the gains coming after CEO Reed Hastings reported subscriber base growth that impressed investors. While there's no solid catalyst behind today's pullback, Netflix's stock is about 20% more volatile than the broader market. Not to mention that it's only natural for some people to cash out after such a remarkable run.