American Title: "Sparks Fly for Magnemite".
This episode reveals Pikachu is afraid of being abandoned by Ash.
After the numerous Magnemite and Magneton clear the station of Grimer, Misty notices there is still a Muk left in the control room. Ash then says, "An adult Muk, and its child!" But, there is no Grimer in the room. Also, he refers to it as "an" adult Muk, even though it was the only Muk nearby and they had seen it only a few minutes beforehand. They refer to it as if it is a new arrival. These errors only occur in the dub.
Ash sends Muk to Professor Oak's Laboratory due to its nasty smell. However, the stench appears to be a non-issue when Ash calls on Muk in subsequent episodes.