On the shelves of a laboratory near San Francisco sit tanks and tanks of mysterious-looking liquids. Labels identify some as simulations of human heads, while others relate to muscles.
It sounds like the ghoulish headquarters of a mad scientist, but it isn't. It's the Silicon Valley offices of UL, a product testing organization previously known as Underwriters Laboratory, and these liquids play an important part in smartphone safety.
You might not know UL, but you can probably find its logo on a number of products around your home.