|Marion putting on stilts resembling horse legs and performing a communication ritual with a horse|
She prepared herself for this by injecting herself with small doses of the serum to build up her tolerance for it, until she could finally take a full dose of "horse plasma containing the full spectrum of foreign immunoglobulins", whatever the heck that's supposed to mean.
Anyhoo... this, according to the Art Orienté objet folks, caused her horse and human blood to be bonded which turned her into a human-horse hybrid, or some such thing. Marion Laval Jeantet said of her experience, "I had the feeling of being extra-human. I was not in my usual body. I was hyper-powerful, hyper-sensitive, hyper-nervous and very diffident. The emotionalism of an herbivore. I could not sleep. I probably felt a bit like a horse."
Um... OK. Sounds reasonable to me.