As you progress in the game, you earn achievements as you pass wrapping milestones, and there is a panic inducing ramp-up in speed of the conveyer belt as you get further too. Each box has one or two dotted lines indicating where to apply tape. The game is quite sensitive to your input, and so you can apply tape a few degrees off the required line. If it's too divergent, or you completely miss the box, you'll lose one of your three lives.
Another way to lose a life is to tape a box that has a bomb icon. These packages are presumably sent along to make sure you're paying attention! They're the perfect hazard for a game like this because it is easy to fall into a trance like state and play with a degree of muscle memory. It's easier than you'd think to tape a bomb box before you realise what it is!
Another reason to hold yourself back slightly is for the double wrap bonus. Here you score more points if you can cover two horizontal markers in one swipe.
Overall, Wrap The Box is great fun and really addictive. You can find it for £1.50 in the Nokia Store.