The Professor drinks the fermented berry juice even though, in "Nyet, Nyet, Not Yet", he said he was allergic to alcohol.
Near the end of the episode, all the castaways are passed out cold when Lord Beasley finally catches his butterfly. Right after saying the line "That's the trouble with you Americans - you simply don't know how to hold your tea" as he's exiting off camera, Mrs. Howell starts to open her eyes slightly, but then quickly shuts them again. Perhaps she thought the cameras stopped rolling.
The butterflies are obviously plastic props on clear fishing line.
Throughout the show Lord Beasley refers to the Pussycat Swallowtail as the rarest butterfly in the entire world but in the radio interview he says there's an even rarer butterfly in the Antarctic.
Apparently, no one thought of asking Lord Beasley to allow his boat to pick up the castaways and leave him to hunt his butterfly.