How on earth did a chicken leg bone get into my garden

I saw Dylan walking back to the house in a low sort of squatting fashion, all four legs bent, body low to the ground, he's never done this before. He looked in real pain. He left something odd looking on the lawn. He came in and threw up a little. I went out to see what was on the lawn and it was a chicken leg bone. Unless there were more bones, I'd say he threw up what he had and left the rest in the garden. We haven't had chicken legs for a couple of weeks and I'm very careful about chicken bones.

This isn't the first time I found chicken bones in my garden. Where on earth are they coming from? Could it be cats or magpies dropping them? It's bin day today so maybe they dropped something.

Dylan is now hiding under my chair.