Biting or Pinching
The Hydration Engine responds both to biting and pinching.
If you look at the bite valve, it looks very similar to other bite valves. However, the bite valve of the GEIGERRIG is designed to handle the pressure. Therefore it doesn't leak.
(The bite valve also has an "on" and "off" position should you choose to use this feature. Not necessary though as the bite valve holds back the pressure until activated by biting and pinching.)