Looks pretty real to me...they didn't have cgi back in the 40's. However, if they could do that then why wouldn't they still be doing it now with better technology?
The point of contention is the decapitated dog. The actual neck of the dog is never shown. At points it lifts its head. The "explanation" is that it's a sedated dog with its body covered up.
Isn't similar technology used to great extent during difficult surgeries? Where the patient is basically dead and all the life functions such as breathing and blood circulation are performed by machines.
