As anyone who has seen the movie will tell you, the Eraserhead baby is the stuff of nightmares.
The baby itself is famous for being somewhat of a mystery. David lynch refuses to discus the baby, what it is, how it was created, or why it’s so gosh darn creepy. The few comments he has made have been cryptic. Statements such as “it was born nearby” or “maybe it was found” have lead to rampant speculation including theories that it could possibly be such things as a skinned rabbit or a cow, lamb, or even human fetus.
The prop itself, nicknamed “Spike”, featured several working parts making its eyes, mouth, and ears capable of independent operation.
What is the baby actually made of and what evidence do we have to prove this?
The answer to that question is; no one will ever know. David Lynch knew he was onto something ethereal, so he prohibited any promotional photos of the baby and forced his SE crew to sign a release saying they could never talk about it. Lynch, himself, has always been elusive at best. All anyone will ever have is speculation, until Lynch decides to spill the beans.
I want to add that the idea that the baby was living tissue has 2 main roadblocks; decomposition and Rigor Mortis. It is highly unlikely the baby was actually living tissue, though it may have been modeled on such. I have seen mention that it somewhat resembles a sheep fetus, so that may have been the vision Lynch worked from. Lynch would have needed several such fetuses for multiple days of filming, which just doesn’t seem plausable.