Example 1
Donald Trump sneezed like a gorilla.
You can't sneeze something. The act of sneezing can't really be transferred to anyone or anything. That's what makes "sneeze" an intransitive verb. No objects here.
Example 2
Casper evaporated into thin air.
You can't really evaporate someone or something; evaporation is something that happens on its own without anyone doing it. That's what makes evaporate an intransitive verb.
Example 3
Forrest Gump ran all over the country.
Forrest just...ran. Like, you heard him: he just felt like running. Forrest's act of running isn't transferred to something or someone else, so run here is intransitive.
Note: The type of "run" in this example is different from the "run" in a sentence like "She ran the entire office." In that context, "run" is transitive.