Galen’s anatomical demonstrations on living animals constitute a justly famous chapter in the history of scientific method. This essay, however, examines them as a social phenomenon. Galen’s demonstrations were competitive. Their visual, cognitive and emotional impact (often expressed by compounds of ѳαῦμα and ἔκπληξις) reduced onlookers to gaping amazement. This impact enhanced the logical force of Galen’s arguments, compelling competitors to acknowlege his intellectual and technical preeminence. Thus, on the interpersonal level, Galen’s demonstrations functioned coercively. On the philosophical level, Galen was using a rhetoric traditional to Greek science, a way of arguing that involved a unitary view of nature and an emphasis on homology between animals and man. But he was also using a rhetoric of power and status differentiation articulated via the body. As played out in the flesh, public vivisection resonated with other cultural practices of the Roman empire: wonder-working competitions, judicial trials, and ampitheater entertainment.