well this city gal wants to know how do you tell the difference between hay and straw?

hay is grass, harvested green, and allowed to dry. straw is grass that has dried in the field..
both are dried grass.... do they look different? feel different? smell different? (hay has more nutricion than straw.. i only have book knowledge of the stuff- You wouldn't want me to go buy a supply, cause i would know good hay from bad straw!)