Did Jake grow a ponytail in five minutes? Did he instantly shift his butt over to the other side of the seat? Did his hat suddenly become longer so it covered more of his hair?
From that sequence I posted, it only shows one head going left to right, not two next to one another.
I see no dummy in that sequence.
Only one person.
In the beginning, Jacobs head and arm move, and as the plane starts to tilt, Rosa reaches over to him.
She would not reach for an inanimate object on the outside aisle of the seat.
And besides, the sequence does not show two heads sticking up over the back of the seat; no room for two bodies/heads.
Ref your post #244 you mention mannikin
http://www.freerepublic.com/focus/news/3428362/posts?page=244#244
“...That mannequin was sitting straight-up on the outside-most side of the seat while Jake sat straight up on the interior-most side of the seat...”