You're on the bus or train, okay? And you fancy a quick game of something on your iPhone or iPod touch to pass the time.

Sounds reasonable, after all you need to drown out the man talking so loudly into his mobile that the person on the other end has to hold their handset 2 feet away from their ear. And a teenager that's listening to the latest Usher album, not through headphones - that would be soooo 90s, grandad - but via the mono speaker on a crappy phone.

However, you can't play a driving game as the tilt controls force you to fling out your elbows like a Dutch footballer and you're squeezed between a jolly, but rotund, lady and a business chap reading the Financial Times.

Nor can you play an FPS as the tapping of the screen may irritate the old lady sat opposite, who is staring at you incessantly, and you're one of the rare breed who actually considers those around you.

Nope, you're going to have to settle for a puzzle game. But what game, you ask?

Scarabeus: Pearl of Nile

iPhone/iPod Touch
Currently 59p (£1.79 normally)

Based on a game previously available for Windows Mobile and PocketPC devices, Scarabeus: Pearl of Nile is a cunningly simple puzzle game in concept, yet becomes fiendishly difficult after a few levels. And as there are 40 of them, it'll certainly keep you going for a while.

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You have to spin rotating dials in order to guide coloured marbles through an interlinked maze. In the centre of each dial is a correspondingly-coloured scarab beetle which, after four marbles have been placed around it, will disappear with a flourish. Get rid of all of the scarab beetles and the level's complete.

However, the mazes will also become peppered with hazards. Some will change the colour of the balls, some might only let certain colours pass through, and there's an intermittent trapdoor that can occasionally appear. There's a stack more, but we wouldn't want to spoil any surprises.

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Certainly, with the ball juggling you soon find yourself in the midst of, Scarabeus is not exactly relaxing. Indeed, at times, it can instigate more panic than an alarm clock in a discarded ruck sack.

But, that's the appeal. It's a game that will have you as transfixed as you are frustrated, as resolute as you are bamboozled. And for 59p (its current sale price) it's an absolute shoo-in.

Altogether now: "Scarabeus, Scarabeus, will you do the fandango..."