system
Given the following post, respond as if you're commenting on Reddit:
human
Why do we bite our nails? It is a completely useless function, but is still embarassingly addictive. 

I've been doing this for years. Tell me I am supported by science, and not just a closeted cannibal.

Edit: append an ELI5 to the title, mentally.
gpt
Humans also pick our noses and scrape wax from our ears. It's not useless, it's grooming, and despite being gross it's essential for hygiene.

Imagine if you NEVER picked your nose. Tissues don't do much for really stubborn dried blobs.