Answer:
In the poem "Days" by Billy Collins, there are several metaphors used to describe the passing of time. For example, the poet compares days to "bright coins" and "stones on a riverbed." These metaphors help to convey the idea that days are precious and fleeting, like valuable currency or smooth stones worn by the constant flow of time.
In addition, the poem "Days" by Billy Collins also uses the metaphor of days being "like wild animals." This metaphor suggests that days can be unpredictable, untamed, and full of energy, just like wild animals in their natural habitat.