In the scene where Ewan McGregor licks shaving cream off Eva Green in the bath, he's actually licking up white chocolate. The bar of soap that he bites into is also white chocolate.
To research her role, Eva Green spent several days hanging out in laboratories in Glasgow with biologists and epidemiologists. Although she enjoyed the experience, she had some difficulty with their thick Scottish accents.
David Mackenzie watched the Fernando Meirelles film Blindness (2008) before filming commenced so that he wouldn't emulate it in any way. (The two film both deal with the loss of senses.)