Vladimir Demikhov’s experiments were controversial primarily due to ethical concerns about animal welfare and the invasive nature of his procedures. Creating two-headed dogs and performing complex transplants subjected animals to significant suffering, as many of them lived only briefly after the surgeries. The experiments also sparked debates about the morality of pushing scientific boundaries at the expense of animal life and well-being. While his work was groundbreaking and contributed to advancements in organ transplantation, critics argued that the methods were inhumane and questioned whether the scientific gains justified the ethical costs. This controversy highlights the ongoing tension between scientific progress and ethical responsibility.