I'd like to imagine there was originally no murederous stuff goin' on in that shed, Flutters just asked everyone not to come into the shed to test if they trust her and absolutely EVERYONE went in the damn shed, not a single exception. Lassie puts up a note on the door that says "Please do not enter, anyone" for no reason whatsoever except for the fuck of it and proceeds to find all of Equestria within the shed alll at once. That'd drive anypony insane.