The thousands of extras required for the movie “Seabiscuit” aren’t people. Nor are they computer generated. They’re blow-up dolls – not that you could tell… “At a time when filmmakers are increasingly relying on digital imaging and special effects, the blowup extras represent something of a low-tech throwback. It recalls an earlier Hollywood era when production problems were solved through old-fashioned ingenuity, not high-tech trickery. Like so many interesting innovations in movie history, the inflatable dolls were born out of filmmaking necessity.”