I believe the correct answer is: D. The author humanizes the prion with playful language by saying "[i]f it manages to burrow into a corner."
In this excerpt from "Mad Cow, Furious Farmer”, the example in which the author keepings a lively tone even while discussing a disease is:
"[i]f it manages to burrow into a corner."
As opposed to the terminology author uses (such as: bovine spongiform encephalopathy (BSE)), the informal language of more commonly understandable comparison gives the lively tone to this excerpt, even though he is addressing the serious disease. Other example of this would be: "a little bit squishy and maybe a little bit sticky".