I am willing to believe that my unobtainable sixty seconds within a sponge or a flatworm might not reveal any mental acuity that I would care to call consciousness. But I am also confident […] that vultures and sloths, as close evolutionary relatives with the same basic set of organs, lie on our side of any meaningful (and necessarily fuzzy) border—and that we are therefore not mistaken when we look them in the eye and see a glimmer of emotional and conceptual affinity.
"Can We Truly Know Sloth and Rapacity?" pp. 389–390 - Leonardo's Mountain of Clams and the Diet of Worms (1998)