Do we know why Nelson says "epidermis means your hair"?

Question

In Bart of Darkness, we have the following dialogue starting with Bart standing on his treehouse:

Nelson: Hey Bart, your epidermis is showing!

Bart: It is? [Bart looks in vain for the problem, only to overbalance and fall from the treehouse, then screams with a girlish scream]

Nelson: [talking to Kearney as Bart plummets] You see, "epidermis" means your hair. [Bart lands with a thud] So technically it's true; that's what makes it so funny.
_{(Source: Wikiquote)}

It's incorrect because

... epidermis is the outer layer of the three layers that make up the skin, the inner layers being the dermis and hypodermis.
_{(Source: Epidermis, Wikipedia)}

What I'm curious about is why Nelson says this, as it seems just as funny if he said "epidermis means your skin" and more accurate.

Question: Do we know why Nelson says "epidermis means your hair"?

I'm wondering if this was intentional (it may have made the quote more well-known), or if it was just a mistake by the writers.

Answer 1

The joke is that Nelson is playing a prank that depends on Bart’s ignorance of the word “epidermis”; but it turns out Nelson is just as ignorant as his target