It's so simple. Like most block puzzlers out there your task is to match colours (or in this case coloured animal heads) into horizontal or vertical rows of three or more.
You're presented with a grid of jumbled heads to match on the bottom screen and you're able to swap two adjacent heads in order to create your rows. However, you can't just swap any old blocks; you can only swap them if you're going to score from the move.
The difficulty (especially later, when the pressure is on) is finding a potential scoring move before the time runs out.
On the top screen you have the all-important score, the maddening driving force behind the game, the 'lucky' animal for that level (which gives you double the score), and the animal count needed to progress to the next level.
Play is against an ever-decreasing time bar. Combos of two or more cleared clusters of animals increases the score a little. Gaining levels increases the meter significantly.
You also have three 'lives' - binocular icons that, when you're flummoxed about where to make your next move, give you a life line to get back into the scoring swing of things.
That's pretty much it - there are other modes that basically revolve around the same concept, but on the whole things remain consistently true for each. It's ludicrously addictive. If we're honest, Zoo Keeper has been the most-played game in the office despite being rudimentary.
It does have some flaws in so far as the difficulty curve isn't quite steep enough, making games last for a touch too long as you improve, but there's no denying it's become a firm favourite round these parts.
Zoo Keeper is out for DS on 11 March