The cel number is C-13, and the seller says it's 
the end cel. I only counted eleven cels used in 
the scene (some were probably reused, because 
when he talks his mouth just goes back and forth 
between 3 or 4 different positions). So that 
makes me think that maybe they originally planned 
for the scene to be longer, but then somewhere in 
the filming and editing process they changed it 
and didn't end up using this cel. 
Of course, that makes it hard to be *sure* that 
it's real. But it looks pretty authentic, and it 
doesn't look like the kind of thing someone would 
try to fake.