[ See, this would be awkward if America wasn't... America. And if he knew how things worked. THANK GOD GERMANY HELPED CLARIFY HOW HUMAN REPRODUCTION WORKS. ]

Sexual maturity. You guys reproduce, so you gotta go through puberty, right? Okay, so you're a guy, right?

[ He pauses a moment, looking at Eridan as though he needs confirmation for this fact. ]

It's when your voice gets lower and you start getting hair on places other than your head and you get random boners and other stuff.