Looks like a joke, but it's not.  This ad for an Australian movie to be released on August 16 kicks off a survey of mutant/monster animal terror films at Cryptomundo.

Such movies never did anything for me, I must say.  To me, they're all just sort of boring (and usually stupid) and not worth wasting time on.  However, the thought of mutant killer sheep really cracks me up.

Note they don't so much fly as plummet...