Carbon dioxide

A colorless gas, carbon dioxide has a faint, sharp odor and a slightly sour taste. Each molecule of carbon dioxide consists of one atom of carbon and two atoms of oxygen. Its chemical formula is CO2.

Spines

Any hard pointed defensive projection or structure 

Sprout

To grow, spring up, or come forth as or as if a sprout. : to send out new growth. 

Underground

Beneath the surface of the ground. 

Shrink

Become or make smaller in size or amount; contract or cause to contract