Descartes' conception of bête machine relies upon his mind/body distinction, which has been fallen victim to many criticisms over the years, such as that of the problem of interaction. As Princess Elisabeth of Bohemia once pointed out, in order for Cartesian system to retain its validity, there must be a way in which the body (an extended material substance) and the mind (an unextended immaterial substance) interact with each other (Robinson, 2016; Skirry, 2014). Descartes found himself completely perplexed by this problem; his ultimate candidate for this point of interaction in the pineal gland proved unconvincing (Skirry, 2014). To this day, metaphysicians are grappling with the mind/body problem, which suggests that Cartesian Dualism rests upon a faulty foundation.
Descartes also presumes that the mind is responsible for our distinctly 'human' and intentional actions, and thus relegates unconscious mechanisms to that of the body. However, since there is nothing preventing complex thought patterns and human rationality from being mere mechanisms of the brain, there is little reason to suppose that animals could not have thoughts as automata, nor that humans are free from being dictated by mechanism (Huxley  2002: 218).
Moreover, it is peculiar that humans possess immaterial souls and animals do not if the theory of evolution is to be believed, as it runs into a problem of continuity; humans evolve from simple, unconscious mechanistic organisms with corporeal souls, only to develop into the first beings on Earth with consciousness and incorporeal minds (Allen & Trestman, 2015; Wilson, 2014). Of course, Descartes would simply assume that this was a result of some divine intervention, but this is yet another occult property that does not align with our current understandings.
With this in mind, we could instead suppose that consciousness originates from the brain, in unity with the body. Seeing as many other animals have been observed to possess brains, it isn't unreasonable to suggest that animals are simply less conscious than human beings, rather than all animals being considered as completely unconscious machinery, and that human beings have simply developed a more sophisticated consciousness through a gradual process of evolution. This destroys the distinction between both mind/body as well as between human beings/animals, as they could both conceivably exist in the same sense as conscious automata.