Just to be sure what we're talking about here, did this worm come from your dog or cat? If so, did they vomit up the worm or pass it in their stool? If the worm is smooth and does not appear segmented, it is most likely a Roundworm. Roundworms are one of the most common intestinal parasites of both cats and dogs, being even more common in younger pets or pets that have a lot of exposure to the stools of other dogs and cats.
You should have your veterinarian do a stool check on your pet to firmly establish the diagnosis and talk with you about the best treatment and ways to prevent a re-infection.
I covered Roundworms in my weekly blog and you can read about them at: http://questionsondogsandcats.blogspot.com/search/label/Roundworms
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