Sherlock Holmes notices that someone is wearing a different brand of deodorant and deduces they're having an affair. In reality, there are dozens of reasons why they could have made the switch. Perhaps, for example, they just saw that Lynx advert that promises one squirt and they'll be chased along a beach by a dozen bronzed bikini-clad goddesses. So rather than dealing in absolutes, psychologists like Texas University's Sam Gosling look for patterns in behaviour that point to a meaningful trend. For example, when you're at someone's home for the first time, you'll no doubt be drawn to the pictures they've framed and hung on their walls. Chances are they've chosen these images from a bank of many more, so what do these choices say about them? Look at what they're doing in the photographs and notice any common elements, such as family closeness or a desire to be seen as a sporty, active type?