Note Flash used to be a normal single headed pony, but an accident in his Alchemy Lab left him with two heads.
Since it would be confusing for everypony to refer to both heads by the same name they decided to split their name between the two of them.

On their right (our left) is Note and to their left is Flash.
An interesting quirk to this head split is that Note Flash used to be Bilingual speaking standard equish(english) and mexicolt(spanish),
but ever since they split Flash only speaks in Equish and Note only in Mexicolt.
Both heads understand both languages no problem… but for whatever reason they can only speak with the language that was assigned to each head.