Secondo me non tutti riescono a fare il movimento ottimamente perché non tutti riescono a muovere le orecchie. Il punto non sta nell'aggrottare la fronte, ma nel far avanzare in avanti lo scalpo, mossa che provoca il movimento delle orecchie ma che non tutti sono in grado di fare. Curiosamente ho trovato una osservazione di ciò in un testo molto famoso:
Some few persons have the power of contracting the superficial
muscles on their scalps; and these muscles are in a variable and
partially rudimentary condition. M.A. de Candolle has communicated
to me a curious instance of the long-continued persistence or
inheritance of this power, as well as of its unusual development. He
knows a family, in which one member, the present head of the family,
could, when a youth, pitch several heavy books from his head by the
movement of the scalp alone; and he won wagers by performing this
feat. His father, uncle, grandfather, and his three children possess
the same power to the same unusual degree. This family became
divided eight generations ago into two branches; so that the head of
the above-mentioned branch is cousin in the seventh degree to the head of the other branch. This distant cousin resides in another part of France; and on being asked whether he possessed the same faculty, immediately exhibited his power. This case offers a good
illustration how persistent may be the transmission of an absolutely
useless faculty, probably derived from our remote semi-human
progenitors; since many monkeys have, and frequently use the power, of largely moving their scalps up and down.
The extrinsic muscles which serve to move the external ear, and
the intrinsic muscles which move the different parts, are in a
rudimentary condition in man, and they all belong to the system of the panniculus; they are also variable in development, or at least in
function. I have seen one man who could draw the whole ear forwards;
other men can draw it upwards; another who could draw it backwards;*
and from what one of these persons told me, it is probable that most
of us, by often touching our ears, and thus directing our attention
towards them, could recover some power of movement by repeated trials.
(Darwin, The Descent of the man)