Here's why:
* Noun: A noun is a word that names a person, place, thing, or idea. "Laugh" refers to the action of making a sound of amusement or joy.
* Pronoun: A pronoun is a word that replaces a noun. "Laugh" doesn't replace a noun, it names the action itself.
Example:
* "Her laugh was contagious." ("Laugh" is the noun, the object of the sentence)
* "I couldn't help but laugh." ("Laugh" is the verb, describing the action)