For this project I “fed” two coots in an Amsterdam canal my personal belongings, like a picture of my parents, my photo negatives and old toothbrushes. I was interested in the way things that I value for certain reasons would be valued by another species, and what this would tell me about the relativity of all the stuff we care for. These birds where already used to making their nests out of plastic trash (actually they thrive in Amsterdam because of the amount of trash, one expert told me). I took quite some time before the birds got used to me and would accept my gifts, they clearly had a preference for some objects over others.
(I of course cleaned everything afterwards)