You know, I think this is one of the few episodes where Ash, Misty and Brock were tricked by Meowth without looking like complete idiots. I mean, Meowth didn't speak the human dialect at all, and the only thing that might give Meowth away is his standing on two feet, which even then, seeing how the Meowth in this episode is the first time that the twerps actually encountered a Meowth other than Team Rocket's Meowth, that didn't matter much, anyways.
Of course, when Meowth basically blew his cover by saying "That's right", Misty was the first to catch on. Sometimes I get the feeling that Misty's the only one to actually see through Team Rocket's disguises most of the time (Ash doesn't seem to see through them for the most part, and Brock seemed to see through disguises only if Nurse Joy/Jenny was involved. Even then, he was fooled by Cassidy when she disguised herself as Nurse Joy, and it was even implied in Fire and Ice [the first time he "saw through" a Nurse Joy disguise] that he didn't actually see through it and only said that "his radar never failed" to save face.).
Sometimes I kinda wish that Sugimori did not change his Meowth Artwork to match that of Team Rocket's Meowth, since it was explained that his standing on two paws instead of the usual four was a result of wanting to become more human and was NOT normal Meowth Behavior.