Re: 4th Season Stargate Atlantis - Trio - 5 star poll - SPOILERS AHOY !

From the Collected Witterings of Martin, volume 23:
>  The zats for example. Why have them kill at all? Why 3
> shots disintergrate? What does that do that two shots don't?

The answer to the zat question is "energy dissipation".  One jolt disrupts

your cells enough to stun you.  If you're hit a second time before the 
effect of the first blast wears off, the ***ulative disruption is fatal. 
Hit a *third* time, and it becomes sufficient to completely disrupt atomic

bonds.