Humans see faces everywhere – two dots on paper, a man in the moon, or Jesus in a bagel. This is known as pareidolia, and an interesting part of it is the corollary: it gets grim when you think about things like talking bacilli. Tiny Invaders is about an army of alien germs infesting human bodies, grinning and making goo-goo eyes every squelch of the way.
As anyone raised on How Your Body Works knows, human innards are mostly tubes and angry white blood cells, and in Tiny Invaders they're arranged in circuit-like patterns that overlap at many points. You shoot a number of germs (dependent on the level) along these tracks from a central 'invader', changing their route at intersections and gathering as many orbs as possible before returning to the launch point to drop them off.
Winning a level requires you to collect every orb, and golden orbs increase your number of germs by one when returned, so hitting the top completion times is a matter of picking the right path. Before each level starts there's as much time as you want to plan, and this simple touch is enough to keep the many swings and roundabouts of Tiny Invaders manageable – later levels are filled with speed pads, teleporters, and cloning objects that are almost too much to manage even when you have planned your germs' approach.
Tiny Invaders' only misstep is in detecting your taps in these more frantic moments. Tapping is used for both speeding up and switching gates, and when the distinction between these two is fine then the game seems to get it wrong as much as you do, barrelling an innocent party of germs into antibodies one too many times for our liking.
That said, the best pleasure in Tiny Invaders isn't really the white-knuckle action. It's those moments spent mentally sketching its levels out before launching into them and executing perfectly – or getting smooshed. Infesting humans slowly and inexorably with an army of cheerful germs – Tiny Invaders isn't perfect, but it definitely brings a smile to your face.