When it comes to snakes, there are very few internal parasites that you can identify by looking at the outside of your snake (or by observing its behavior). In fact, heavily parasitized snakes often have very good appetites, but the just fail to put on weight. Most internal parasites are too small to be seen in the feces with the naked eye. That's why Fons is suggesting that you take a stool sample to a vet... and because tropical snakes are often imported with heavy parasite loads. If yours is captive born, the odds of it being parasitized aren't as great.