What is hey is for horses?

The phrase "hey is for horses" is often used to tell someone to stop saying something that is unimportant or irrelevant. The origin of the phrase is unclear, but it is believed to have been used as a dismissive response to children who would call out "hey!" when trying to get someone's attention. The phrase is a play on words, as "hey" is also a type of grass used as animal fodder, particularly for horses.