Headcannon One:-

Percy loved his first trip to zoo. All the fish talked to him cheerfully, and the ice cream was delicious. But his favourite part was when a brazilian boa escaped, scared a fat boy while a thin boy with a lightning shaped scar stood by.

Headcannon Two:-

 On the first of September, Percy was at King's Cross Station to catch a train back home. He remembered going up to a boy with a lightning scar and saying, while pointing at the scar, "Zeus thought I stole that once." 

(🔝🔝I know this will probably never happen cause Percy lives in America but whatever.)