If one of the input arrays has a duplicate entry, a spurious intersection will be detected.

An input array set of

my @array1 = qw(c d e);
my @array2 = qw(e f g h);
# my @array3 = qw(a b d);  # original code
my @array3 = qw(a a b d);  # modified for test
my @array4 = qw(s g h j k l);
[download]

Produces output of

@array0, @array1: e - 1
@array0, @array2: a d - 2
@array0, @array3:  - 0
@array1, @array2: a - 1
@array1, @array3: g h - 2
@array2, @array3: a - 1
[download]

godevars may be dealing with input arrays that have unique elements; certainly, his example data has this characteristic. However, it is nowhere stated explicitly that this is the case, so I just thought I'd mention it.