This scar is the result of the removal of his conjoined twin. They had to emergency fly him from Kenya to Hawaii quickly after he was born in an attempt to save the twin. Unfortunately this was not possible and it’s the reason he hides his birth certificate.
You joke but digest this a moment. Senior's third wife had a son named David Opiyo Obama. "Opiyo" means elder or first twin. David is the one who *supposedly* had a motorcycle accident and died right before Barry showed up in Kenya in the 80's. No one can find David's birthdate or death date but he was *supposedly* around 18 or 20ish. In "Dreams" when Barry shows up in the village and a man stops to talk to him thinking he's David but Auma tells him that David died. "Dreams" (page 338) says the man looks as if he's seen a ghost. Below, on the left, is *supposedly* David as a toddler. Does that little boy look familiar?