This is a fairly simple illusion... all you need is:
-Wood for a box and stand
-2 square mirrors (must be exactly the same)
-Spinal chord, painted
I've attached a simple diagram of how the illusion is created... Simple put the bloody spinal chord were the two mirrors meet in the middle. Use a jacket and an attached shirt/vest to blend in the spinal chord "into the actor" to really pull off the sell.
I hope this helps. -Tyler