He got a taxi license and took real taxi driver shifts for Taxi Driver.
He became a proficient saxophone player for New York, New York.
He lived in Sicily for a time before taking on Godfather II.
So when a filmmaker named Alex Berry, a finalist in Snapchat Shorts at the Tribeca Film Festival, made a short film using De Niro (who introduces himself as “Bob”) and some Snapchat filters, it’s clear the actor has inhabited the mind of a C.G.I.-animated dog, a flower child, a panda, and a weird thing with a weird voice.
When he licks, it’s as if he’s lived among dogs, and when he says something inscrutable using the “voice changer,” it’s like he’s been speaking only in squeals for months.