Beware Of Food You Pick Up Off The Ground (拾い食いに気をつけろ, Hiroigui ni ki o tsukero) is the one-hundred and twenty-ninth episode of the Gintama anime.
As Sadaharu suddenly loses his appetite, Kagura takes him to a hospital for pets. There, they also encounter Katsura who is there because Elizabeth is in bad health. Sadaharu and Kagura stay there overnight to be sure that Sadaharu gets well. Around this time an old dog who is on the verge of death is in the hospital too, so Kagura decides to take this dog to its owner.
With Sadaharu's loss of appetite, the Yorozuya take their dog to a vet. The veterinarian notes that Sadaharu most of eaten something out of the ordinary which caused him to lose his appetite. An x-ray of Saduharu's stomach reveals that a human arm protruding from a dirt pile was the cause. Fearing that they'd be arrested, Gintoki and Shinpachi try and lead Sadaharu out of the vet causing the arm to stick out of his mouth. Kagura yanks the arm out, revealing it to just be a sex doll. Although Sadaharu is feeling better, he's still suggested that he stay the night in the vet for precautionary sake. After Shinpachi and Gintoki leave, Katsura with Elizabeth greets Kagura. He reveals that Elizabeth isn't feeling well due to her swallowing a middle-aged man during one of her walks. While he plans on getting surgery to get the middle-aged man from Elizabeth. They overhear the veterinarian discuss a matter about an old dog with the son of its owner.
That night, Kagura stays overnight with Sadaharu at the vet. Unable to sleep she remembers the old dog that the veterinarian was talking with the son of its owner. She finds the dog hyperventilating in a cage that Katsura was sleeping next to. Katsura then discloses the dog's backstory and they figure that he wants to see his owner again. Once released, the dog attacks Katsura and surprising talks. The dog claims that he's been emancipated from the Old Man's control. During his audacious declaration, he starts to cough and begs for an ambulance to be called. A flashback from 18 years ago reveals that the dog is really a star devouring parasite called Parasite X. By infecting multiple hosts it devours the planet to nothing and it planned on devouring Earth. The parasite's plan is foiled as it only managed to only infect a puppy belonging to an old man. The emotional dog goes on another tirade in front of Katsura and Kagura about his predicament at a restaurant. Although Kagura believes they should ditch the dog, Katursa believes that they should help it atone for its sins. It's at that moment, Parasite Z the antithesis to Parasite X confronts the dog. Parasite Z in the body of a cat accompanied by a horde of cats stages an ambush on the dog. Meanwhile, two of the three sons to the old man, leave the youngest son in charge of overseeing their father.
Returning the ambush, the group try and escape by riding on Sadaharu. Katsura then sacrifices himself to try and fend off the cats, but fails. Back to the old man in the hospital, he wakes up and knocks out his youngest son. The old man then says that it's time for a walk.