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.
A literary genre is a category of literary composition. Genres may be determined by literary technique, tone, content, or even (as in the case of fiction) length. Genre should not be confused with age category, by which literature may be classified as either adult, young-adult, or children's.