In the first dream sequence, Little Ricky at first is wearing a hat with rabbit ears. At one point, Lucy picks him up to take him to Ricky, who is being lured away by Carlota; as she does, the hat falls off. The problem is that the episode's editors used a close-up insert of Little Ricky without the hat a bit too early--before Lucy picks him up--then returned to a wide shot where he's still wearing the hat. Once the hat falls off, the same (or similar) hatless close-up is used again, this time making sense with the continuity.
Ricky says that he and Lucy have been married for 12 years, but it's previously been stated that they've been married for 13 years.