Last weekend, Dale picked up a new ewe, named Josie. All the dogs gave her the once over and went 'yeah, okay, not a real sheep' and went on about their business (sleeping and mooching treats).
Not Rosie. She took a look, took another look, then went to her default 'I don't know what the heck that is so I'm gonna bark my head off at it'. She's 6 months old. This is normal.
Eventually she took a hint from the rest of the hounds and ignored it
When in doubt, fall back and bark...
...Then go see if it's edible