Bookcase sneezes

Last post I said I didn't expect any activity until Autumn. I guess I was a bit premature. Last Thursday my wife and the older dog were in the library, my wife using the computer and the dog snoozen beside her chair. I was directly across from my wife in the Den working on a drawing with the younger dog sitting with her nose almost touching the TV screen in the far side of the room. The TV was turned low as the dog follows the action not the sound anyway. The younger dog is a TV freak whereas the elder male could not possibly care any less. Anyway, it was relatively quiet when the southern wall bookcase sneezed. It wasn't my wife, it wasn't the sleeping dog it certainly wasn't me or the other dog. "The book shelves sneezed", my wife said, "Did you hear that?" " The bookshelves?" I replied, I figured it was her. "I didn't sneeze" she protested. Hurriedly I jammed on a pair of shoes and quickly left by the western side door of the house, ran around back and checked out the area where those bookshelves front the exterior wall. Nothing, nobody anywhere to be seen. Had someone sneezed outside the house I doubt we would have heard them anyway unless a window was open and we haven't been able to open a window into the Library in years. I came back in reporting nothing to report. "What area of the bookcase did the sneeze emminate from?" I inquired? Pointing at the second glass door from the west or directly south of where she sat, "There". We've been through this before. Several years ago, while being visited by a friend we all heard the bookcase cough. This was during winter and we had a good coating of snow on the ground. The friend remarked, "I think we have some snoops". He wanted to go out and try to track them down; he thought he knew who they probably were. So we left, this time by the eastern rear door which opens directly out behind the eastern wing of the house where the Library is located. There was not a trace of footprints in that virgin snow, not even animal tracks. This time there was no snow. I drilled behind the bookcase shortly after the first episode to see if I hit any hollow areas; I didn't. We do not know who or what coughed then and we certainly do not know who or what sneezed this time. One interested party suggested that perhaps we have or had an animal in the walls that caused the sneeze. For those of you who are not familiar with this house, it is brick and it would seem an opening large enough to admit a raccoon would be easily spotted. I won't say it couldn't have been an animal; possibly that is the answer. But how?This house, built in 1857, has solid brick walls several bricks thick. The early builders plastered (what they used for plaster back then was pretty close to concrete by todays standards) right over the brick, The floors are local hardwood and we have found that the use of wood studs in this house, originally, was pretty sparse except for the floors and the dumwaiter shaft. The roof has huge walnut rafters as well, but not much wood in the walls except for rooms that were added. If there are hidden areas in the house that I haven't found they must really be well concealed. We have 5 hidden (rooms)actually not big enough to be rooms but great places to conceal loot. Two of them are filled with insulation (Blown in insulation filled these speces before we were able to determine where in heck all of that insulation was going) There is one innerwall tunnel that leads from a crawlspace under the stairs all the way up to the attic but the exit in the attic was closed off and plastered over, from the looks of it, very early in the houses history. So I suppose anything is possible.Old houses can be a lot of fun....if you're not easily scared.