It is an example of
A. poetic language
'Zero at the bone' is an idiomatic expression from Emily Dickinson's poem. It's an allusion to a basic, chilling fear.
Poetic language is the use of any poetic/literary language techniques. They are used by poets to convey their intended message in their works. Some of the most common examples of poetic language techniques are : metaphor, simile, symbolism, personification, imagery.