The tone of “To a Mouse” is primarily remorseful, though toward the poem’s end the tone grows slightly embittered. The poem’s remorseful tone appears most clearly in the speaker’s contrition over accidentally destroying a mouse’s nest. The speaker expresses his remorse in lines 7–12:

     I’m truly sorry Man’s dominion
     Has broken Nature’s social union,
     An’ justifies that ill opinion,
               Which makes thee startle,
     At me, thy poor, earth-born companion,
               An’ fellow-mortal!

These lines demonstrate that the speaker’s remorse has more than one layer. Most obviously, he’s apologetic about the physical act of destruction he’s personally wrought. Yet in this stanza he also links this act of destruction to a larger and even more ruinous tendency that’s bound up with “Man’s dominion” over the earth. This dominion “has broken Nature’s social union” and created antagonism between humans and other animals. The speaker is evidently sad that the mouse has a justifiable instinct to flee from humans. Yet for all the speaker mourns the mouse’s fate, the mouse is also a symbolic stand-in for the speaker himself. Indeed, the remorse he feels ultimately relates to his own uncertain fate. That he believes his own fate is in fact worse than the mouse’s fate becomes clear in the slightly embittered line that opens the final stanza: “Still, thou art blest, compar’d wi’ me!” (line 43).