Ouzo was used as a replacement for absinthe for the drinking scenes filmed on the first day. Because the scene turned out so well, method drinking was adopted for the rest of filming. As a result, Thewlis had admitted in a interview that he can't really remember making the film at all.
In the Café Andre where the adult Isabelle Rimbaud meets with Paul Verlaine, the typeface on the window is clearly in Helvetica, a typeface that was not created until 1954.
Arthur Rimbaud: [to Verlaine]
We should make a bargain. You help me... and I'll help you. If we go away together, I'm sure you'll be able to start doing good work again. And when we've taken as much as we can from each other...