This article, influenced initially by a reading of Carrie Rohman’s Stalking the Subject: Modernism and the Animal (2009), shows how the interpretation of some passages of the The Book of Disquiet, written between 1913 and 1934 by the modernist poet Fernando Pessoa, suggests a critique of broadly understood Western anthropocentrism and humanism, which is supported by a precise and recurrent reduction to the absurd (reductio ad absurdum is the erudite expression used in Pessoa’s text) of a very specific version of the post-Darwinian environmental humanity, identified mainly with animals and plants.