Milk Carton Mystery ...

It's possible that I'm the only person on the face of the Earth that washes the inside of a milk carton before tossing it into the recycle bin. Hi ... I'm your OCD friend.

So the routine is this:

1. Open the lid
2. Fill the carton about 1/4 full with hot water
3. Shake
4. Pour out
5. Repeat steps 2 through 4
6. Toss into recycle bin

The magic happens in step 3. When you shake a milk carton that's 1/4 full of hot water, the air inside expands. When you take the lid off to pour (that's step 4, BTW), pressurized air forces it's way out.

The only reasonable explanation that I can come up with is that the heat of the water causes the air inside the carton to expand and pressurize. I know ... it's weird, but try it.

I'd be interested to hear your hypothesis (that's nerd for guess).