[Digging into his pocket, Sans makes a bit of a show of thinking on the answer to that question. When his hand finally emerges again, holding a small wrapped gumball, he swipes it across Frisk's chest where their sweater stripes should be. They were a kid, after all.]

What it sounds like, kid. [He finishes the bit by handing the gumball to Frisk, straightening up with one more thoughtful glance Kaworu's way. His eyelights reorient on Frisk after a half second.] Watch where you're running, alright? No reason your mom's gotta know about this, but I'm kinda honor bound by Mom Law to tell her if it happens again.

[Another look towards Kaworu. This time, he even speaks to the guy.] You've met Tori, right? Tall, big arms, lots of fire magic to crisp up bad guys.

[The 'so make sure you're not one' implication is clear, no matter how friendly Sans' tone is.]