The 17th century Japanese poet Basho, considered by most to be the first haiku master, once told his students: “The old verse can be about willow. Haikai requires crows picking snails in a rice paddy.” 

*haikai refers to the popular poetic form of the time, renga, of which the opening stanza or hokku eventually evolved into the haiku

that old willow

dripping sap

all over my car