use Data::Dumper;

use strict;
use warnings;

simple_call(
      animal => 'monkey',
      fish   => 'tuna',
      insect => 'ant',
      insect => 'spider'
);

##########################
sub simple_call {
    my %params;

    while(my($key, $value) = splice @_, 0, 2) {
        if (exists $params{$key}){
           if (ref $params{$key} eq "ARRAY"){
              push @{$params{$key}},$value;
           }else{
              $params{$key} = [$params{$key},$value];
           }
        }else{
            $params{$key} = $value;
        }
    }
    print Dumper \%params;
}