In "Jellyfishing", in the beginning, when Squidward walks out of his house with his bike, Spongebob says "Hey, Squidward" but his mouth is saying something different. See more...
In the episode "Karate" when Sandy is about to pour the hot sause over Spongebob's tongue, the face on the sause that laughs and taunts Spongebob is Tom Kenny, the voice of Spongebob. See more...
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SpongeBob SquarePants (1999) - 5 with pictures
Screenshots of mistakes that have been online for less than a year are only visible to members, but the rest are available to everyone. Don't forget to check out the picture of the day, updated daily, and the top 30 screenshots too.
Updates: Series 2