It also had to do with trying to make the thing itself less important to look at

A Wax Mold of the Knees of Five Famous Artists.

"Although it's made out of fiberglass, and they are my knees.
I couldn't decide who to get for artists, so I used my own knees. Making the impressions of the knees in a wax block was a way of having a large rectangular solid with marks on it. I didn't want just to make marks in it, so I had to follow another kind of reasoning. It also had to do with trying to make the thing itself less important to look at. That is, you had to know what it is about, too. To go and look at it was to try and thin k whether you liked to look at it, or just how involved you were in looking at art in general; that was not quite enough though, you had toknow these other things too."

---Bruce Nauman, interview with Joe Raffaele and Elizabeth Baker, 1967