POPCORN!

 

The popcorn started to pop and it expanded

 

. The hull of the popcorn protects it.

 

In the hull where the endosperm is the storch to expand.

 

The pop from the popcorn is the steam escaping in from the hull.

 

The popcorn has water inside.

 

it and when the water evaporates it expands the hull.