It Must Be True! is an episode from the second season of Garfield and Friends.
Garfield hosts a TV show where he makes things up and says they're true.
Over at WBOR studios, Garfield tells the viewers that fire hydrants actually contain compressed water rather than being connected to the water lines, and that they are manufactured in a factory in Walla Walla, Washington. They are then bolted to the street so pets can use it as a toilet. Odie doesn't believe it, so Garfield blasts him with the compressed air from his hydrant. It turns out Garfield is on a TV show called "It Must Be True", a show where anything he states is the truth.
The next thing Garfield states is that Wyoming does not exist. In 1789, Arbuckle Vespucci, famous explorer, was working on his map of the United States and left out Alaska and Hawaii, which his cat put on. There was also one gap left out, and there were no more pieces. So the cat wrote in "Wyoming", which was Italian for "no state here".
Next, they state that cows speak English literature when no one is around, as exampled by two cows talking about A Midsummer Night's Dream until the farmer walks by, in which they act like regular cows. After that, they claim raisins are not made by drying grapes in the sun. They're made by shrinking bowling balls. Then, they state that all ottomans contain breakfast items.
Finally, Garfield claims that dogs have no brains, as shown when he x-rays Odie, showing only a sign that says "This space for rent". To his shock, there are a lot of dogs in the audience who are offended by that remark. Garfield tries to add in that they don't harm cats because cats are poisonous creatures and if they attack one, they'll be poisoned as well. They don't believe it and chase Garfield off stage where they beat him up for insulting their kind while Garfield makes up more stuff to save face. After the thrashing he took, Garfield vows never to lie again, indicating that everything he said on the show was a lie. The narrator does his bit only for Garfield to tell him to stop before passing out.