In "Butcher Shop," what tone is created by the poet's use of imagery?

In “Butcher Shop”, Charles Simic creates a tone through imagery that’s spare, realistic, contemplative and violent. It’s important to note that throughout the poem very little actually happens – it’s rooted in observation. Only in the first two lines (“Sometimes walking late at night/I stop before a closed butcher shop”) and the last two lines (“Where I am fed,/Where deep in the night I hear a voice”) is there any kind of action, hence the contemplative aspect of the tone – he’s merely observing and thinking.
The realism and sparseness are found in the mundanity of the objects he observes: the apron, the knives, the wooden block. Nothing really out of the ordinary here – it’s everything you’d expect to see in a butcher’s shop and nothing more. What those objects evoke in him, though, causes the poem to take a dark turn. The last line of the first stanza – “Like the light in which the convict digs his tunnel” – calls to mind images of capture, imprisonment and the hope of escape. The repetition of “blood” in lines 2-4 of the second stanza suggests not only violence and death but a sense of enormity – the “great continents” and “great rivers and oceans” of blood become almost overwhelming. Finally, the “wooden block where bones are broken” caps off the violence and causes us to realize that what we’re reading is an act of witness of sorts. The stillness and sparseness of the scene belie the brutal actions that take place there at other times.