In the season one He-Man episode "Teela's Trial" we see the common pairing of Beast Man and Trap Jaw. Beast Man is oddly silent in the episode and does not speak a single word, whilst Trap Jaw talks constantly throughout. However in one scene, the steel-jawed villain's voice changes very noticeably, as if another character is present! Close inspection of the script reveals something very interesting; originally it was supposed to be Trap Jaw and Tri-Klops who were paired up in this episode. This explains that the voice change is because it is Tri-Klops talking, not Trap Jaw, and also explains why Beast Man has no dialogue in the episode whatsoever! It is obvious that there was not enough appropriate animation of Tri-Klops for this episode, prompting the Filmation artists to replace him with Beast Man, and force his one piece of dialogue over to Trap Jaw!
For your listening pleasure, Trap Jaw with Tri-Klops' voice!