One of the subtler pieces of symbolism in this movie is the spiral staircase in Vincent's and Eugene's house, which is designed to resemble the DNA double helix. Some SPOILERS follow:
- A common term for the person Vincent has become is a "borrowed ladder". Vincent is borrowing the house, and specifically the upper level, from Eugene along with his identity.
- When Vincent moves into the house, Eugene lives on the lower level, at the bottom of the ladder/helix, while Vincent lives on the top. Following his accident, Eugene has reached the bottom of his genetic potential, while Vincent uses his genetic material to climb to the top of that potential.
- When the police inspector comes to the house looking for Jerome/Vincent, Jerome/Eugene has to make the incredibly difficult climb up the stairs to the top level using only his arms. He has to borrow the "borrowed ladder" back from Vincent and climb to the top to be Jerome again, achieving his own potential through a physically demanding activity. (I guess all that Olympic swimming paid off.)
- Finally, when the police inspector descends the stairs to see what's on the lower level, Vincent is already there hiding behind a pillar. Vincent is literally hiding behind Eugene's "borrowed ladder" to keep his true identity out of view of the police and his own superiors.