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Some interesting replies there.
Mojo, I couldn't decide if that blackbird was trying to skin the slug so that it could eat the insides, or if it was trying to discard the insides in order to eat the flesh. The video cut off too soon.
Rowanwitch - that sounds like a tidy way to dispose of unwanted gastropods.
As for my blakbird, it has become too tame for its own safety. Yesterday I saw it sitting on the path outside my neighbour's back door - right up against the cat flap! Talk of living dangerously. Today I was fitting a new lock on the back door and it was left ajar whilst I went upstairs for some tools. When I returned, the blackbird had come right into the house and was flapping against a closed window attempting to go out again.
It is probably just as well that I won't be able to feed it for the next few days. It will then have to re-learn how to be a wild bird and forage for itself.