Cats should not be allowed outdoors. Period. Especially when the domesticated feline is an extra from The Matrix.
Yes, there will be those who will think that the mockingbird had it coming but what the mockingbird was doing was defending its territory, which likely included a nest with young, from what it judged (obviously correctly) was a threat. Had the cat been kept indoors this whole encounter never would have taken place. Cats do not belong outdoors precisely because of situations like these.
Warning! This video contains footage of a bird getting caught by a cat. If you don’t want to see such a thing may I suggest something cute instead?
If you have a cat that you allow outdoors please keep it indoors. You can get some tips on how to make your cat an indoor cat here.