How to write Pact contract that matches to key 'x' either object of type Y or Z

I try to write a pact contract test covering following scenario. I have a consumer calling an GET to receive an information about an animal, either a cat or dog.

response1:
{
   "animal" : {
      "type" : "Cat",
      "meow" : true
   }
}

response2:
{
   "animal" : {
      "type" : "Dog",
      "barks" : false
   }
}

In code both Cat and Dog are subtypes of an Animal class. Is there a possibility to write a contract expecting response to contain "animal" key with value matching either cat (expecting properties "meow" and "type") or dog (expecting properties "barks" and "type").

In other words. Is there a possibility inn Pact's Dsl to declare that under the key "animal" there can be either an object of definition X or an object of definition Y?

No, you have to write two separate tests to cover this scenario to prove that your code can actually handle both cases. Think of if you were to write a unit test that took an Animal as an argument, but behaved differently depending on the animal - you'd need to test it with all of the variants.

The argument is similar to why we don't support optional attributes (see https://docs.pact.io/faq/#why-is-there-no-support-for-specifying-optional-attributes).