Self Heating Obento

I took a holiday that involved a shinkansen bullet train journey last week.  On the platform I grabbed the nicest looking obento to eat on the way.  By chance I stumbled on a self heating beef obento.

The deal is, you pull a string that is sticking out of the cardboard box and after 7 minutes of steam and heat, your obento is ready.

It all relies on the chemical block that sits under the plastic tray of food.  Apparently ripping out the cord, activates a chemical reaction which generates enough heat to almost burn your lips. 

Very handy, very cool and very wasteful.  I enjoyed it but the environment can’t afford too many of these things.