Actually that appears to have been at least partly the point. The site says "[E]r wollte wissen welchen Gesichtsausdruck man macht, wenn man zum Beispiel starke Bauchschmerzen hat," or "he wanted to know what facial expression one makes when one has, for example, extreme belly pain."

My German is not quite equal to the task of figuring out if he actually sculpted using freshly-dead corpses as models, but there are several references to extreme pain.

The reason for his interest in abdominal pain: he apparently suffered from lead poisoning, which may well have contributed to his death at age 47.

That self-portrait bust, "The Artist Introduces Himself, Laughing," is 43 cm high, and made of lead.