Como Johnny Bones responde corretamente, ninguém jamais saberá. John Patterson, um crítico de cinema do The Guardian declarou:
The secret of the Eraserhead baby is the Holy Grail of Lynch
obsessives, and the one thing missing from Greg Olson's otherwise
admirably comprehensive biography of Lynch (David Lynch: Beautiful
Dark). And yes, it was the first thing I looked for. But one does
learn a lot about the circumstances of Eraserhead's conception and
six-year gestation. There was the birth of Lynch's daughter Jennifer,
with two severely malformed feet, which required several unpleasant
surgeries and the child's incarceration in a "massive, waist-high
cast..."
http://www.theguardian.com/film/2008/sep/06/davidlynch
A razão pela qual menciono essa citação é que um perfil do Guardian de Lynch e seus filmes afirmou:
Most of the film, though, deals with the birth of a mutant baby, a
theme which Jennifer Lynch, who was born with club feet, now feels may
have had its origins in her father's domestic situation: "There is no
doubt in my mind that there is something there that correlates to the
baby in the film."
http://www.theguardian.com/film/2008/sep/06/davidlynch
Portanto, há uma possível explicação - o bebê é representativo, de alguma forma, de sua própria filha (também vale a pena notar que o casamento de Lynch foi interrompido 18 meses após a filmagem do filme).
O item Top Trivia no IMDB ( encontrado aqui ) afirma:
The mutant baby was apparently created from the embalmed fetus of a
calf, although David Lynch has never confirmed this or described how
he articulated it. During filming when he watched rushes, he even had
the projectionist cover his eyes when takes with the baby were
playing, so that no one would know how it was made. After completing
the film, Lynch reportedly buried the "Embalmed Calf" in an
undisclosed location. At the wrap party, they had a mock wake for it.
No entanto, ele não cita nenhuma fonte para essa informação e, portanto, é impossível determinar qual é a probabilidade disso.
Um blog on-line, Cinevistramascope , discutiu-o em um recurso sobre os principais monstros em filmes, concluindo:
The meaning of the baby and the movie remain elusive - saying
Eraserhead is about the fear of fatherhood is a start, but it doesn't
begin to explain everything. Lynch is famously reluctant to discuss
the meaning of his work; with Eraserhead, he has always refused to
explain how he created the baby as well, which has helped it retain
much of its power. The thing looks like a crude puppet, but it has a
sticky organic quality as well that has led people over the years to
speculate that it's made from a cow fetus or other once-living tissue.
I Googled "cow fetus" and don't think that's what it is (also,
blechhh), but that the idea is even worth fact-checking says all you
need to know.
Finalmente, se estiver interessado, um fórum sobre Snopes foi criado para discutir exatamente isso. Eles têm uma seleção variada de opiniões, mas a resposta é simples:
Ninguém sabe realmente porque David Lynch não confirma ou nega nada.