Deliberate mistake: At the beginning of the movie Mr. Coates tells his wife that he will be gone "all of three months, maybe four." The first time we see Bud and Elizabeth Searcy she tells Travis that her dog is pregnant and that Old Yeller is the father. We then see her dog that does not look very pregnant. The next time we see Elizabeth she presents Travis with one of the pups. The problem is that the pup that was supposedly just born is about 4 months old.
Continuity mistake: During the slow-motion sequence, Speedy slams the mallet on the cat's paw and leaves the mallet on the ground when he rescues the mouse. When he puts a stick of dynamite on the cat's tongue, the mallet has gone.
Continuity mistake: When we see a close up of the photo that Jerry has taken, look at the rug that Spike is lying on. You can see that it is completely different to the one when Jerry was taking a photo of Tom putting a chicken under Spike's arm earlier in the short.
Continuity mistake: When the Big Bad Wolf arrives at the House of Straw, there are handles on the doors when he enters. But in the next shot, the handles have gone.
Continuity mistake: When Ned is pretending to be invisible, he pulls out one of the cat's whiskers and there are now five whiskers on the cat's face. But when Ralph is on the champagne cork and is swallowed by the cat, the cat now has six whiskers again.
Continuity mistake: When Bugs is performing his juggling act, he is juggling with four balls. But when the balls fall into his hat, there are now five.
Revealing mistake: When Speedy Gonzales is watching Sylvester drink Tabasco sauce from the tank that sends him miles into the horizon, watch Speedy's tail: it disappears before the scene ends.
Continuity mistake: When Bugs is trussed like a roast pig, the Tasmanian Devil puts salt and pepper on him and he leaves the salt shaker on the tree stump next to Bugs. But when the Devil unties Bugs later on, the salt shaker has disappeared.
Continuity mistake: When Quackie is at the cafe with Mary, their dog is sitting on the chair between them at the table. But when Inspector Faraway appears, the dog has gone.
Continuity mistake: When the Tasmanian Devil passes by the hamburger stall, you can see there is nothing next to the radio on the counter, but when we see a close-up of the radio in the next shot, there is now a mustard pot and a bottle next to it.
Continuity mistake: When Sylvester is unable to sleep at night, the camera pans in on his eyes and you can see that he has his head on the pillow when this happens, but in the next shot he is lying flat out on the bed.
Continuity mistake: When Yosemite Sam says "I dares" to Bugs, you can see there is nothing behind Bugs, but in the next shot he is standing in front of a mountain.