Here you can see some of the many Moais at Rano Raraku.
The one in the front is an exception to all the others on the island.
This one has his head askew from the shoulders.
All the others have a "straight" head on their shoulders.
It is believed (but of course not proven) that, since all the Moais are different from each other - like all people are as well - the carvers tried to make the head look like the guy they wanted to "copy" and this guy had probably a
crooked back or shoulder.