An alien dog is an alien animal in space throughout Planet 51. The Xenomorph dogs chase Chuck Baker after he lands onto the Planet. They use toxic to release themselves from traps like the chain and the leash. One dog was fooled by the mailman with the donut causing himself to get angry and start attacking him. The Alien Dog has similarities to the Xenomorph from the Alien Series and the name of the dog is Ripley as in Sigourney Weavers Character in The Alien Series