The Breeding Center Secret - S1-E55
Revealing mistake: When Butch takes Todd's camera, it is layered behind Todd's hands. (00:15:05)

The Breeding Center Secret - S1-E55
Revealing mistake: After Misty says Team Rocket broke into the breeding centre to steal Pokémon, Team Rocket's hands remain on the bars when they are disappointed. (00:18:23)
Answer: There are a lot of fan theories around this, but the most common theme is that Pikachu had another trainer before Prof. Oak, who gave him to Ash. Pikachu didn't appreciate being handed over.
Ssiscool ★