Pigeon.Lion.Tiger.Elephant SOME_DATA (Key1)
Pigeon.Lion.Tiger.Monkey SOME_DATA (Key3)

##</code><code>##

use warnings;
use strict;

my %hash = (
    'Key1' => 'Cat.Mouse.Game.Lion.Tiger.Elephant',
    'Key2' => 'Cat.Mouse.Game.Lion.Tiger.Lion',
    'Key3' => 'Cat.Mouse.Game.Lion.Tiger.Monkey',
);

while ( my $data = <DATA> ) {
    chomp($data);
    my $value = join '.' => ( split /[\s.]/, $data )[ 1 .. 3 ];
    print map { "$data ($_)\n" if $hash{$_} =~ /$value/ } keys %hash;
}

__DATA__
Pigeon.Lion.Tiger.Elephant SOME_DATA
Pigeon.Lion.Tiger.SeaLion SOME_DATA
Pigeon.Lion.Tiger.Monkey SOME_DATA

##</code><code>##

Pigeon.Lion.Tiger.Elephant SOME_DATA (Key1)
Pigeon.Lion.Tiger.Monkey SOME_DATA (Key3)

##</code><code>##

Pigeon.Lion.Tiger.Elephant SOME_DATA (Key1)
Pigeon.Lion.Tiger.Lion SOME_DATA (Key2)
Pigeon.Lion.Tiger.Monkey SOME_DATA (Key3)