I've run through hundreds of pounds of jalapenos over the years for Taco and Tequila Tuesday and have run across the same issue. Typically when making pico I'm using 4-6 of them so law of averages takes over. An old wise messican once told me it had to do with how much water they received while growing the peppers. The less water, the hotter the pepper. Is it true? Hard to say. I typically make a regular batch of pico and then one with some habanero to wake it up a little bit.

If you want to get really gutsy (pun intended) add a ghost pepper to the mix. That will eat a hole in whatever you try and contain it in, including you. Crazy hot!