Revealing mistake: In the intro of this episode, a glitch is visible.
Blue's Clues (1996)
1 revealing mistake in season 3 - chronological order
Starring: Aleisha Allen, Steve Burns, Seth O'Hickory, Traci Paige Johnson
Continuity mistake: The package Steve received from Mailbox is briefly visible before Mailbox comes in. You can also see a crew member's hand holding the package as Steve grabs it.
Steve Gets the Sniffles - S2-E1
Trivia: During a mailtime segment, there's a rare Blue's Clues poster visible.