error while accessing object retrieved from mongodb using mongoose

mongoose1.js

// mongoose1.js

// Store a json object with a schema less property
// then retrieve them

var mongoose = require('/Users/sarneja/projects/node/node_modules/mongoose/index.js');
var colors = require("/Users/sarneja/projects/node/node_modules/colors/colors");

console.info("mongoose loaded: " + mongoose);

var myConnection = mongoose.connect('mongodb://localhost/test');

var Schema = mongoose.Schema
  , ObjectId = Schema.ObjectId;


var BlogPost = new Schema({
    author    : ObjectId
  , title     : String
  , body      : String
  , date      : Date
  , fbObject  : {} // allows me to store any object
});

var PostModel = mongoose.model('Post', BlogPost);

var firstPost = new PostModel();

firstPost.title="This is my First Post";
firstPost.body="qwq";
firstPost.date=Date.now();
firstPost.fbObject={ // this is the random schema less object
	"id":"1121",
	"name":"asa",
	"aert":"a",
	"pnumber":"12"
};

firstPost.markModified('fbObject');

firstPost.save(function (err) {
  if(err){
  	console.info("error while saving: ".red + err);
  	throw err;
  }

  console.info("saving a post");

});

PostModel.find({}, function (err, docs) {
	if(err){
	  	console.info("error while finding: ".red + err);
	  	throw err;
	}

	docs.forEach(function(doc){
		console.info("POST: ");
		console.info(typeof doc.fbObject);
		for(var i in doc.fbObject){
			console.info(i + " - " + doc.fbObject[i]);
		}
		// Next Line fails!! it says that doc.fbObect is undefined. WHY???
		console.info(doc.fbObject["aert"]); 
	});
  
});