People make maps in Team Fortress 2 specifically for grinding achievements. Bleak, joyless rooms of endlessly spawning bots and resupply crates, where people don't play the game, they game it. But in one of these, achievement_all_v4 , the author's added a surprise. A violent, horrific, hilarious surprise of biblical proportions. Here's a clip.

You can grab the map here if you want to try it locally, or sort TF2's server browser by map name to find any servers running it. It's not easy to trigger the catpocalypse, though - people on the Facepunch forums have been decompiling the map to figure out how it's done. Poster belink offers this guide:

"In both corners next to the respawn cabinets next to the striped walls, there's a func_breakable (keep shooting it - it makes a glass noise). Once you've broken that, under it is a button that triggers 'kittygedon'. I guess you need to trigger them both with +use. I might be missing something, though.."

In fact, here's an awesome clip from scout101547 of the Facepunch guys figuring out exactly how to trigger it - in case you can't hear them, you need to set the server variable "tf_player_allow_use 1" to be able to use the hidden switch. Be warned, though, the cat's appearance sometimes crashes the server.

achievement_all is a real series of achievement-grinding maps, so unwitting players who've shown up to farm some meaningless accolades tend to be somewhat surprised by this turn of events. It's not clear whether this version is made by the real author of the previous maps, and he's just sick of the people who use them, or if this is some inventive griefer showing up and exploiting the name. Part of me likes to think it's Valve.

Team Fortress 2 creator Robin Walker tells us:

"We would dearly love to be able to claim that as our work, but once again the community shows it's much smarter than we are. We were in tears in the office here when we watched the first video.

I'm hoping the creator makes him/herself known so we can award them with a community item."

If anyone knows who the creator is, please have him get in touch with Robin so Valve can sort him out with something nice.

Turns out the creator of the laser death cat map was the very man who uploaded the video. He's updated the description to say so, and he's got in touch with Robin and been given his community item. He also thanks us. Hurray!

Can the cat be killed? Craig tried with his over-powered rocket launcher - probably the most damage ever pumped into this thing - and this was the result:

Craig found a server running the map, and I jumped in with him to get some shots. It's... it's... oh God.