In the beginning of the episode, Pikachu's Pokéball has a lightning bolt on it but it disappears later on.
When Ash enters Professor Oak's Lab and looks at the Pokéballs, the writing is Japanese. When Ash picks up a Pokéball, it's not in Japanese. Later in the series, regular Pokéballs never have writing on them.
In 'Pokemon, I Choose You!', Ash sees a Ho-Oh flying over the rainbow. Yet in 'Pokemon Emergency', the picture he points to on the Pokemon Center's wall is of an Articuno.
In the Pokérap at the end of the show, in the first set of Pokémon listed, the rap names "Poliwrath" but shows a picture of a Poliwag. Later in the rap, it shows the same picture correctly labeled as Poliwag. This Pokérap is played at the end of other episodes throughout the series.
In the poke rap at the end of the episode, Poliwrath is said, and the name Poliwrath is displayed, but the picture that accompanies it, is that of the Pokemon Poliwag. It is noticeable since they use the same picture moments later when Poliwag is said.