It’s always nice to read unusual haiku/senryu. When poets share something original, they have stronger voices. This is the case with this poem.
It paints a picture of neglect, maybe melancholy, and simplicity. Perhaps the poet noticed his or her cracked fingernail while sorting through the fridge. Though we don’t know exactly what is going on (which is good thing to practice in haiku), the tone of the haiku is that of something gone wrong. It seems that the poet has neglected herself or himself for some reason.
It is an interesting fact that only sandwiches are mentioned. It means that the poet lives a meager existence. So, in the poet’s humble life, something has gone wrong. But using the word “forgotten” I lean towards it being depression–a feeling of loneliness.
The poet envisions the depth of his or her loneliness by the crack on the nail and the amount of forgotten sandwiches. One part is something missing (cracked nail), and the next part is dealing with fullness (many forgotten sandwiches): a strong contrast.
The wording is concise and nicely phrased. I think Yumino wrote a poignant haiku that expressed his or her feelings, and of which we can feel as well.
– Nicholas Klacsanzky