Attempting to use JRuby Objects from Java via Red Bridge

Driver.java

import javax.script.*;
import java.io.*;

import interfaces.*;

public class Driver {
  public static void main(String[] args) throws ScriptException, FileNotFoundException, NoSuchMethodException {
    
    ScriptEngineManager manager = new ScriptEngineManager();
    ScriptEngine engine = manager.getEngineByName("jruby");
    
    
    // Import ruby classes
    String filename = System.getProperty("user.dir") + "/ruby.rb";
    FileReader reader = new FileReader(filename);
    
    // Retrieve the object returned by the last line of the evaluated script
    // In this case, a Person object that has a Pet named 'fido'
    Object receiver = engine.eval(reader);
    Invocable invocable = (Invocable) engine;
    
    // Cast the ruby object to the Person interface
    //Person person = (Person) invocable.getInterface(receiver, Person.class);
    Person person = (Person) receiver;
    
    // Retrieve the Person's Pet
    // Two methods for retrieval are shown below, with the second one commented out
    // The first method fails, the second works

    // First method: using interface method getPet()
    Pet pet = (Pet) person.getPet(); // <- Returns an InterfaceImpl
    // NOTE: uncommenting the line below inexplicably causes first method to work;
    //       Just calling invokeMethod on the getter seems to automagically transform the pet variable
    //invocable.invokeMethod(person, "pet"); // Can't call getPet() since invoke goes through Ruby
    
    
    // Alternate method: using invokeMethod on person with method "pet"
    // This method seems to work
    //Pet pet = (Pet) invocable.invokeMethod(person, "pet"); // <- Returns a Pet
    
    // Test the pet variable by passing it to a Ruby function
    // Using the first method, this will fail... Is there a pet.toRubyObject() or something similar I should be calling?
    // The second method works, but what's the point of the interface implementation if I can't use any objects 
    //   returned by its methods?
    boolean isPet = person.askIfThisIsAPet(pet);
    System.out.println("Was the pet a pet?: " + isPet);
    
  }
  
}

Person.java

package interfaces;

public interface Person {
  Pet getPet();
  void setPet(Pet newPet);
  boolean askIfThisIsAPet(Object pet);
}

Pet.java

package interfaces;

public interface Pet {
  String getName();
  void setName(String newName);
}

ruby.rb

require 'java'

class Person
  include Java::interfaces.Person
  attr_accessor :pet
  def initialize(pet); @pet = pet; end
  def askIfThisIsAPet(pet)
    puts 'checking...'
    puts "ancestors: #{pet.class.ancestors.inspect}"
    pet.is_a?(Pet)
  end
end

class Pet
  include Java::interfaces.Pet
  attr_accessor :name
  def initialize(name); @name = name; end
end

Person.new(Pet.new('fido'))