It is the left.
A pun that is also a provocation, as old as the equestrian statue in Terreiro do Paço. The right paw - or the one that is "straight" - is the horse's left paw. The right paw is slightly bent, so it is possible to play with the various meanings of the word "right".
And what color is the white horse? These puns are expressions that together allow for many interpretations and make us think.