Here is the full list of all 51 Left 4 Dead Demo achievements.
Punch a Hunter as he is pouncing.
Rescue a Survivor from a Smoker's tongue before he takes damage.
Kill a Witch with a single headshot.
No Survivors take damage after contacting the rescue vehicle.
You or another Survivor take no damage after being vomited on by a Boomer.
Protect any Survivor from an attacking Infected 50 times.
Survive an entire campaign using only pistols.
Heal 25 Survivors with a first aid kit.
Give pain pills to 10 Survivors.
Revive 50 incapacitated Survivors.
Rescue a Survivor trapped in a closet.
Shove a Hunter off of a pinned and helpless Survivor.
Kill a Smoker who has grabbed you with his tongue.
Kill 10 Smokers as they are pulling helpless Survivors.
Set 101 Infected on fire.
Sneak past all Witches in a campaign without disturbing one.
Single-handedly kill a Tank.
Kill a Tank without it dealing any damage to a Survivor.
Play an entire campaign with no Survivors taking friendly fire damage.
Beat a campaign with all 4 Survivors.
Finish a campaign without ever using a first aid kit on yourself.
Kill a Witch without any Survivor taking damage from her.
Kill 1000 Infected with a mounted machine gun.
Blow up 20 Infected in a single explosion.
Kill 53,595 Infected.
Heal a fellow Survivor when your own health is below 10.
Save another Survivor from a Special Infected while on the ground.
Shove a Boomer and then kill him without him splashing on anyone.
Survive a campaign without being incapacitated.C
Leave a safe room to save an incapped teammate and bring them back safely.
Survive any campaign on Expert.
Survive all campaigns on Expert.
Survive a campaign with no Survivors taking damage from Special Infected.
Light a Witch with a Molotov.
Light a Tank with a Molotov.
Kill an Infected with a single blow from behind.
All Survivors complete a campaign without being vomited on.
Make 100 headshot kills.
Headshot a Hunter while he's leaping.
Survive the No Mercy campaign.
Survive the Death Toll campaign.
Survive the Dead Air campaign.
Survive the Blood Harvest campaign.
Cover four Survivors with Boomer bile at once.
Drag a Survivor 100 feet with your tongue as a Smoker.
Constrict two Survivors on one life as a Smoker.
Pounce two different Survivors on one life as a Hunter.
Kill all four Survivors on one life as a Tank.
Dole out 5000 total Survivor damage as a Special Infected.
As an Infected, incap a Survivor who has entered and left a safe room.
Fall victim to the infection.