Headshot Expert Trophy in Uncharted 3: Drake's Deception
Defeat five enemies in a row with headshots
How to unlock Headshot ExpertSee 100 Headshots for a description and pointers on headshots in general and combine those elements to pull off 5 headshots in a row.
You could use a range of tactics to ensure you unlock this in whatever form suits you best but there is a full proof method that I found to work a charm and can be put into practice just about anywhere where you have the appropriate weapon and at least one enemy. All you have to do is pull off a headshot and then 'Save Game'. After it's saved, go to 'Load Game' and you will be put right back to before you killed the enemy but the headshot will have registered.
For reference, I used this method in Chapter 5 - London Underground in the library. Once you activate the cutscene which shows Nate hanging from the golden statue in the middle column of the library, a couple of bad guys run in. Take them out and 3 more will appear and you will resume things already in cover. You have a silenced pistol that is a single fire round, take aim at any one of them and squeeze off a round for a clean headshot. They will be occupied with Sully and Cutter so you wont take too much damage while lining up your shots either. When all 3 are dead, do the Save and Load trick to save your headshots and repeat. If you mess up and accidentally kill one of the guys then miss out the Save part and just Load up again.
An alternative to this, in case their movement is causing you problems is to use Chapter 16 - One Shot at This. After the part where the jeep slips from your grasp and busts through some chain-link gates in a cutscene, take cover behind the nearby central pillar. Two bad guys will come to the jeep to investigate whilst remaining at opposite sides of the vehicle. With your silenced pistol, aim for the heads of the quite distanced but stationary enemies taking all the time you need to line up. As your weapon is silenced and they can't see each other, the second guy wont notice the other one die and stay nice and still for you. Take him out then save/load until you have the kills.
Your trophy will unlock when you kill your fifth consecutive enemy with a headshot.