What is ironic about the dogs response to the woman in Ah Are You Digging on My Grave?

In Thomas Hardy's poem "Ah, Are You Digging on My Grave," the irony lies in the dog's response to the woman's grave inquiry about whether he is mourning her. Instead of expressing sorrow or loyalty, the dog reveals that he is actually indifferent and is digging to bury a bone, highlighting the stark contrast between the woman's expectations of loyalty and grief and the dog's self-centered nature. This underscores the poem's themes of unreciprocated love and the futility of human emotions in the face of nature's indifference.