Just seeing docs (never twitted inmy life..) I assume $nt->lookup_users.. returns an array so you need to iterate over element or access directly one as in:

# totally untested!
my @users = $nt->lookup_users; 
foreach my $usr (@users){

   print $usr{screen_name}; #??
   use Data:Dump dd method to see the structure you get back (better t
+han Data::Dumper)
   dd $usr
}
# or directly first element returned
print $users[0]{screen_name};
dd $users[0];
[download]

I just looked here and here

UPDATE sorry the method does not returns an array but an array ref: not big difference but different..

# totally untested! again
my $users = $nt->lookup_users; 
foreach my $usr (@$users){

   print $usr{screen_name}; #??
   use Data:Dump dd method to see the structure you get back (better t
+han Data::Dumper)
   dd $usr
}
# or directly first element returned
print $$users[0]->{screen_name};
dd $$users[0];
[download]

L*