Horses' gums recede with age, leading to longer teeth. A common way to inspect a horse's worth is to check it's mouth, hence the phrase. Receiving a horse as a gift and immediately inspecting its value was considered offensive, much like inquiring about the worth of a present today is rude.
Poetry is the first major literary genre. All types of poetry share specific characteristics. In fact, poetry is a form of text that follows a meter and rhythm with each lines and syllables. It is further subdivided into different genres such an epic poem, narrative, romantic, dramatic, and lyric.
Like other writing genres, poetry may seek to tell a story, enact a drama, convey ideas, offer vivid and unique description, or express emotions. However, more than any other genre, poetry seeks to compact all of its ideas into a brevity of space and time.