Ardith Hinton:

AH> Yes, there is a style of male underpants known as "boxer
AH> shorts"... I think that's what the author was referring
AH> to.

Did not the million-dollar girl wear them (a good movie, if
you ask me)?

AH> I also presume that while this guy was invisible his
AH> clothing may not have been, and he felt rather uncertain
AH> as to what the monsters could see.  :-Q

I presume you have seen James Whale's masterpiece, but not
its sequels, which were more primitive but with better
effects: Invisible Spy, Invisible Woman... Mmmm! --

       https://www.youtube.com/watch?v=iho9FD99nu4

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