I'm not sure but look at murder-based sounds in the story. I haven't read since November so all I could is give you examples of common onomatopoeias: Clank! Buzz! Kaboom! Pow!
It is a complement that can be expressed with a smile.
Answer: In my opinion, I think it's 'cause So that the company will see if your reference is someone related to you or from your past job.
