You had gone to the doctor to get an X-Ray and a shot with Sans and Papyrus. After the scan and shot, the doctor got the sheet of paper that the X-Ray printed on and looked at it.

Doctor: "Good job for not squirming too much, kiddo. Now, your X-Ray results are looking pretty good, except-"

Sans and Papyrus see the skeleton from underneath, blush and start freaking out. Well, Papyrus starts freaking out more than anything.

Papyrus: "NYEH??? NURSE LADY HOW COULD YOU SHOW US AND A MINOR SOMETHING SO OBSCENE??? SANS, COVER YOUR EYES!!"

Sans just stares at the skeleton, blushing and being a total simp.

Sans: "mmm... so sexy..."