Williams walked up to a display, which was not fully enclosed, reached across the barrier, and plucked the index and middle toe from the left foot of a female body, the prosecutor said in court this morning.
He gave the middle toe to an unknown male, and kept the index toe as a "souvenir", posting on social media about the theft.
"... I stole a toe from an uncovered display lol," he wrote in the post on Instagram, along with a photo of the toe.
Police have since recovered the toe from him.
The toes cost approximately $5485 to re-affix.
When asked by police about the crime, Williams said he didn't plan the offending.
"I saw them so I took them, sorry," he said.
He entered guilty pleas to both charges and was remanded to September for sentencing.
Body Worlds Vital is a travelling exhibition of human remains that have been preserved through plastination, their fluids and fats swapped with plastics.
The show arrived in New Zealand in April, the first time it had been in the country.
Dr Angelina Whalley and her husband Dr Gunther von Hagens, who invented plastination in the 1970s at the University of Heidelberg to teach students about anatomy, established Body Worlds in 1997.
Since then more than 17,000 people have donated their bodies to von Hagens' Institute for Plastination, which also sends plastinated specimens to medical schools around the world.
More than 45 million people worldwide have seen the exhibition.
