The mystery of the bread from heaven

Yesterday, sometime in the morning when we were off at the gym, one slice of bread inexplicably showed up on our front walk. I am pretty sure that I didn't put it there, and I trust my wife who says she was equally perplexed when she saw it while going out to the car. When we first spotted it it was pretty much pristine (this picture shows it having sat out one damp night, thus the moist appearance you might have noticed), making it unlikely to have been dragged there by a bird or a squirrel, say out of our compost heap which is located quite a long distance away. It's also rather far from the street
which argues against the idea that some person passing by might have tossed it there for reasons too obscure to ponder. That person would pretty much have had to walk up our walk and place it down for it to have ended up where it did, which seems even more unlikely.
We didn't pick it up, thinking that it would simply be absorbed into the food web by the various mourning doves, starlings, sparrows, squirrels, and other wildlife we have seen foraging in the yard. This too proved to be an odd part of the puzzle, as this lovely nice fresh piece of nutrition was spurned by all. Was there something suspicious about the look of the slice, scaring off the birds, and about its odor, scaring off the squirrels?

The investigation is ongoing.

Update: Well, someone appreciates it, or the half that's left at any rate.