Which of the following symptoms might suggest a roundworm infection?

A roundworm infection in animals, particularly in cats and dogs, can often be identified by the presence of the worms themselves in the animal's feces or vomit. Roundworms are large, typically spaghetti-like parasites that can cause digestive issues and other health complications. If an owner observes either of these signs, it strongly suggests that the animal is infected with roundworms. This is critical for both diagnosis and treatment, as identification of the parasite through fecal examination or physical evidence can prompt prompt veterinary care.

Other symptoms mentioned, although they may be related to an animal's overall health, do not specifically indicate a roundworm infection. Weight gain could be misleading, frequent barking is often a behavioral response unrelated to parasitic infections, and high-energy behavior could simply be a trait of the animal’s personality rather than an indication of health issues. Thus, the presence of roundworms in poop or vomit is the most direct and telling sign of a roundworm infection.