When Huck refers to and the trees with Spanish moss on them hanging down from the limbs like long gray beards he is using an example of what literary device?

Huck's comparison of the trees with Spanish moss to long gray beards is an example of a simile, which is a figure of speech that directly compares two different things using the Words "like" or "as." In this case, the simile helps create a vivid image of the trees covered in Spanish moss.