for example, like a dog that's sad that its walk is coming to an end, a concorde will droop its snoot on landing, and do that face you know the one where you want to give it a little jet-a as a treat
im a big fan of having as many different flight control surfaces, canards, variable geometry wings etc as possible. it really broadens the range of expression the aircraft is capable of, and increases its capacity to react and emote with dramatic or subtle gestures and body language