I was so hoping that @Elmer_J.Fudd was gonna triumphantly announce “Whoosh!”.
Oh well …
FYI keeping the word straight gets easier once you recognize “shelled” is a past tense verb like “peeled” or “diced.”
Installing shells on peanuts would be … difficult. So it means un-installing shells.
One round; one racoon. Seems easy enough to me.
Now how much he tore up the barn first is a different matter. 
“Shelled” is one of those terrible words that can mean both one thing or its exact opposite, like “cleave” or “sanction”. Their use should be made a crime. The OED says “shelled” can mean either “having a shell” or “deprived of the shell”.
I’m tryng to think of anything that you would commonly put shells on
Scoops of ice cream or soft-serve dipped in molten chocolate.
Or, similarly, the candies that are dipped lumps of fondant, caramel, or nuts like e.g. See’s, Whitman, or Lindt make. And a bunch of similar culinary uses.
Beyond that I got nearly ‘nuthin’.
Which was my point. If “shelled” refers to the act of removing or installing a shell well … it damned near has to refer to removing.
Well, okay. 
think this, that carnival game where you shoot at a disc spinning around, except it’s screaming like a banshee
The “having a shell” sense doesn’t necessarily mean that a shell has been artificially added; it can just refer to something that has a shell. Some quotations from the OED use “shelled fish” to mean what is usually called “shellfish”; other quotations given are “those fruits that are shelled, like nuts”, “a bug’s body is shaped and shelled”, “shelled like the rhinoceros”, “the eggs, or rather shelled embryos”, and “some little shelled mollusk”.
Honey, we’re gonna need a bigger shotgun. 
Every one of those sounds to non-expert me like a quote from an 1840s treatise on what they then called Natural History.
None of those sound remotely like contemporary usage, not even high register contemporary usage. I don’t doubt OED’s attestations. I do wonder about their applicability to the modern world.
Except maybe glue traps (if you don’t mind the cruelty).
I do mind the cruelty. Snap traps are very quick, and I’ve had good luck with them.
Yeah, that’s how I am. I tried the humane mouse traps for awhile, until I finally admitted that I was just setting out extra food for the ungrateful little buggers. Snap traps are regrettable but necessary; but glue traps are definitely crueler than I’m willing to go.
Similar to what @Beckdawrek’s dad did, I’ve tied a tiny knot of kitchen twine around the bait spoon and then dabbed peanut butter onto it. Enough of the bait soaks into the string that the mice try to yank it off, and that’s all it takes.
These days, though, I only have two mouse traps. They’re very effective, but expensive: cat food and litter alone run me hundreds of dollars a year.
[Moderating]
A reminder that this thread is in FQ, and the primary question is about why peanuts don’t stick to things.
Alternately, if the OP (@OldGuy )feels that the primary question is now sufficiently answered, we can move this thread to IMHO and let the discussion take its circuitous course.