El Nino is a weather event that happens every 5 years. It leaves Europe largely unscathed but causes havoc around the southern hemisphere. El Nino causes droughts, floods and has even been linked to an increased incidence of war. And yet it is surprisingly hard to predict. Adam speaks to Professor Adam Scaife, from the Met Office, about unpicking the science from weather chaos.

Echolocation is the ability to sense objects using reflected sound. A handful of animal species do this - most bats, some whales and even a few humans. Some blind people use echolocation to navigate the world they can't see. Some make a clicking sound as they walk. Others use the sound of their footfall. In fact, all humans, sighted and unsighted, do it. Adam meets BBC's Damon Rose, who is blind, and they compare skills.

Marnie Chesterton travels to Southampton University's Institute of Sound and Vibration Research to meet Daniel Rowan. His team have recently isolated some of the factors necessary to echolocate. The work involved an anechoic chamber - the quietest place on earth and the sound equivalent of nothing.

Last week Adam gave the incorrect reason for why we have seasons. Dr Laura Rogers, a physics teacher, puts him right.

Dr Rhys Jones, star of BBC TV's Wildlife Patrol talks to Adam about the origin of snakes. A recent paper from a team in Yale hypothesises a common ancestor with tiny hind legs and nocturnal habits. Adam questions why 3400 species of snake have evolved to not have legs, when millions of other animals find them so useful.