Kalauer...

mongodbquery

var pipeline = [
{$match: { 'scored': true }}, 
{$unwind:'$trials'}, 
{$project: { 
	'trials.snippet': 1,
	'trials.condition': 1}
}, 
{$group: { 
  _id: {	
    'condition': '$trials.condition',
    'snippet': '$trials.snippet'}, 
  count: {$sum: 1 }
  }
}];
db.behavior.aggregate(pipeline);