here's the full code:

#!/usr/local/bin/perl -w
use strict;
$|=1;

# www.PerlMonks.org 140734|(Golf) The Animal Game

# ask the question passed, return true or false
sub a($) {
    my ($qu, $ans) = (shift);
    while(!$ans) { print "\n$qu?\n"; chomp ($ans = <STDIN>) }
    $ans =~ m/y/io ? 1 : 0;
};

# ask if animal is passed value, return true or false
sub g($) {
    my ($ani, $ans) = (shift);
    while(!$ans) { print "\nis animal $ani?\n"; chomp ($ans = <STDIN>)
+ }
    $ans =~ m/^y/io ? 1 : 0;
};

# ask what animal, return user input
sub t() {
    my $ans;
    while(!$ans) { print "\nwhat animal?\n"; chomp ($ans = <STDIN>) }
    $ans;
};

# get question to identify animal: 
# true for new, false for old; return question
sub i($$) {
    my ($old, $new, $qu) = (shift, shift);
    while(!$qu) {
        print "\nenter a question false for $old but true for $new:\n"
+;
        chomp ($qu = <STDIN>);
    }
    $qu;
};

# ask to continue, return true or false
sub w() { a('play') ? 1 : exit 0 };

# question/answer data structure: hash of arrays
my %q = (
    "larger than a breadbox" => ['cat', 'giraffe'],
);

no strict;
while(w){($k,$v)=each%q;$k||redo;$u=$$v[a($k)];next if(g($u));while(($
+l,$x)=each%q){next unless$$x[0] eq $u;a($l)?$y=$$x[1]:goto N;goto E i
+f(g($y))}N:$b=i($u,$c=t);$q{$b}=[$u,$c];E:}
[download]

no strict;
{
    while(w){
        # select a question
        ($k,$v)=each%q;
        # try again if no more questions (end of hash)
        $k||redo;
        # ask question, get proper animal from question hash
        $t2=$$v[a($k)];
        # guess animal, end loop if found answer
        next if(g($t2));
        # lookup keys with value[0] matching $t2
        while(($k2,$v2)=each%q){
            next unless$$v2[0] eq $t2;
            # if key exists, ask question
            # if answer negative, ask new animal
            a($k2)?$t5=$$v2[1]:goto NEW;
            goto END if(g($t5));
        }
        # else, ask new animal
NEW:
        # ask new animal
        $t4=i($t2,$t3=t);
        # add to question hash
        $q{$t4}=[$t2,$t3];
END:
    }
}
[download]

~Particle