Now usually when you chuck a Molotov cocktail in a game it results in a couple of your foes wandering around while on fire. Not so in Left 4 Dead.
Valve's latest has petrol bombs that act like the real thing - covering an entire room's worth of floorspace with scorching, visibility-stealing flames.
This is how your correspondent accidentally ignited three of his friends and about 20 screaming, galloping zombies at the exactly the same time in a previously deserted boiler room.
Team-mates were angered, representatives from Valve held their heads in their hands, everybody died. Sorry guys.
The disaster happened inside something that's new to L4D: stand-off areas in which hordes of zombie-kind are summoned through the press of a button.
Turning on a window cleaner's lift, for example, that takes an age to descend to your level and has squeaky gears that prove an inexplicable zombie attractant.
In recent months, an added awareness of the rhythm of zombie movies has infiltrated the game. Intricate pacing has always been a Valve byword, but now the balance is finer.
The safety of the reloading and equipment areas is just as important in the process of keeping your adrenaline pumping as the vast areas where you're at the mercy of the zombies' AI director. Tooling up and moving out is just as important as running away and screaming.
It's pretty much impossible to play L4D without whooping and swearing - it's unending in its non-scripted surprises.
Whether it's seeing a friend charge round a corner straight into the blubbery explosion of a boomer and then drip with its gore as zombies pile around a corner to eviscerate her, or simply closing a door and watch the slavering braindead punch holes in it - levels are an unceasing and outright delight.
Importantly, friendly fire is never turned off - bullets will strike your team-mates. In fact, this was aptly demonstrated when I'd been pinned down by an angry businessman with half a face, and was desperately firing off pistol shots while flat on my back.
The lovely Zoe got the full force of my ineptitude - straight in the gullet. No shadow of a lie, Left 4 Dead is as good as you want it to be.
It's becoming increasingly apparent that any shit game can be rendered half-decent by the addition of co-operative play, but no FPS has ever had it balanced or paced this well.
Or has ever been built entirely around the concept, come to that. Later this year the dead shall rise, and together we will rejoice.