Frodo's Lament for Gandalf was Frodo Baggins' attempt to put his grief at Gandalf's death into words while at Lórien. When he recited it to Sam Gamgee, it didn't seem as lovely as it had in his mind, when he was inspired by elven voices. Sam was enthusiastic about it, however, he thought a verse about Gandalf's fireworks should have been added. He composed the last verse, which is why its rhyme-pattern is different. In The Fellowship of the Ring (film), the last verse, spoken by Sam, is the only part that's included.