my $chicago = { qw(tiger bob munch toy) };
my $wisconsin = { qw(tiger sara munch toy) };
my $rockford = { qw(tiger sara love toy) };
...
my $newIntersection = &intersection($chicago,$wisconsin,$rockford);

OUTPUT
tiger - only common key in all 3 hashes

Also 
my $chicago = { qw(tiger 0 bob 0 munch 0 toy 0 ) };
my $wisconsin = { qw(tiger 0 sara 0 munch 0 toy 0 ) };
my $rockford = { qw(tiger 0 sara 0 love 0 toy 0 ) };

OUTPUT
tiger toy - common keys in all 3 new hashes.