About hallucinations that we can see, if everything looks rather dull and mundane, they are created by our consciousness. We see in the glare of light and so on some fragments, actions and shapes.
In the literal sense, we are talking about the illusion of perception. In particular - about pareidolia. The essence of this effect is the completion of visual information. Our brain is a restless, passionate lover of recognizing patterns and patterns, including where they are not. In the depths of a mirror drowning in a dark room, the brain can easily find a black cat, a hundred monsters, and whatever.
In a figurative sense, the answer can be completely arbitrary, because in the interpretation of metaphors we often rely on that property of our psyche, which was noted in the paragraph above.
So that my answer does not look offensively short, I will add that in terms of sensorics, the brain is generally not inclined to get bored. In order for "boredom" to finally overcome him, either an exceptional monotony of the environment or deprivation of sensations is needed. And if in the first case it lasts a very long time, highlighting more and more subtle nuances in the incoming sensations (remember how many shades the Eskimos distinguish in the snowy desert), then in the second case the conditions turn out to be completely unnatural, the brain is simply not ready for them. You can read about the sad consequences of such an experience on the Internet.
Hence my sincere advice: don't be shy about mirrors and don't let your brain get bored!