Apple's stock fell 6.43 percent today. 

Zero Hedge says it's the biggest Apple drop in four years.

The weird thing is that no one seems to have an answer for why it's happening.

Piper analyst Gene Munster ran through some options (margin requirements, misinterpretation of the news, technical problems, concerns about China) but none of them really add up.

If you've got any ideas, let us know in the comments.

For what it's worth, this is not as bad as it's been for Apple. The stock has been down since September, and at one point it almost fell under $500.


Yahoo Finance screenshot