La Grande Odyssée Savoie Mont Blanc in Switzerland is the toughest international sled dog race in the world due to the topography of the mountain it covers. Each year the race brings together the best mushers in the world. Together with their Alaskan and Siberian huskies, they race over a 900km course. This episode follows several of the teams as they prepare for the race and the challenges it holds. Discover why the husky is the top dog for both stamina and endurance, and how they are perfectly built for rough terrain and extremely cold environments. Over in Queensland, trained odour detection dogs are used to sniff out vicious but tiny invaders. The dogs are mostly Labradors that are trained to accurately detect fire ants. In favourable conditions, they can pick up an ant’s scent from dozens of metres away. The dogs work in extremely warm temperatures and have to work in very short shifts so as not to overheat. Elsewhere this week, Dr Tom Smith explains how he has found a new way of using dogs to track ringed seals in the Arctic. Unusually, the dogs he uses are not large, thick-coated huskies, but Labradors. They are trained to find ringed seal lairs, and in the right wind conditions they are incredibly accurate. Tom and his remarkable team of Labradors are based in Quebec, and this programme joins them as they prepare for their next research expedition to the Arctic.