Contributed by Bill Arning / Plunked in the middle of Matthew Gilbert’s solo exhibition “Pretend Till It Hurts” at Jane St. Art is a five-foot-tall steel construction crane buckling under the weight of a rented bouncy castle. Titled Until the Whole City Falls Over, the sculpture turns an ordinary suburban party rental into something strangely unsettling. Inflatable castles felt perfectly natural at children’s birthdays until Gilbert reminded us what castles actually are: military edifices built to withstand siege and slaughter.