This is the only episode in which the castaways leave the island. And the only episode where they switch bodies.
This introduced a lot of the iconic "Gilligan's Island" "haunted house" musical themes. One is a long, "monster march" played slowly leading to a diabolical-sounding five note, thrice repeated in lower key, fanfare, then coming to a halt with a few small notes. In various combinations and variations these three elements would turn up elsewhere: the first part is when Boris Balinkoff, the mad doctor, comes to the island at the beginning; the memorable "evil" fanfare is first in the castle shots, but also in the torture chamber and one scene in the mind-transpose machine room. Also used a lot is an equally eerie descending electric organ cue that features notes descending. Both, for the majority of the remainder of the season would be recycled for many showings and reruns to come.
The dungeon set is the same set used in the season-three episode of Get Smart, "The Spy Who Met Himself."
A mad scientist on an island who experiments first with animals, then humans, is the basis of the story "The Island of Doctor Moreau". by H.G. Wells. Here the doctor only translated mind and personality. In the original story and subsequent movies, the doctor grafted body parts.