The entire poem presents a perfect example of personification. Look at its title; one could assume that this poem is about someone with human qualities described in the poem. For instance, in the following line below:
Whatever I see, I swallow immediately.
Here mirror swallows the reflections seen on glass. As we know, mirrors do not swallow or eat however, people can.
Second literary device is hyperbole, when mirror says:
Now I am a lake.
This line contains both personification and hyperbole–personification, because mirror speaks like humans and hyperbole because the poet has exaggerated the mirror, which is deep like a lake. However, unlike a lake mirror is very small in size and cannot be deep and endless like a lake.