Steam goes off, lid in the handle slides down to be in airtight mode, and pressure starts to mount again within the sealed pot before the next hiss. At the end of a few hissings, foods are cooked faster than time, with lesser energy burnt. A simple knowledge about "how to manage pressure" led to the invention of pressure cooker by French physicist Denis Papin way back in 1679.

Centuries later, pressure cooker has become the most useful item in every kitchen. Let it hiss, pressure cooker would work fine for you. Choke its hiss, it would go against you by turning itself into a ticking bomb.