[X4U] Overactive contextual menu

[Michel Treisman]

MacBookPro running Mac OS X 10.6.8.  I am using a trackkpad, not a mouse. To see the contextual menu for an item, I Control-Click on the item. The problem is that sometimes the contextual menu pops up when I have NOT control-clicked.
Maybe I just click on some text to start selecting it and immediately the contextual menu pops up and gets in my way. That is not predictable - it may or may not happen.  
I have searched for a setting that controls how to evoke the contextual menu, without success.  Anyone know whether there is a setting and where it is?
Mike