A flea's mouth has two functions: one for squirting saliva or partly digested blood into the bite, and one for sucking up blood from the host. This process mechanically transmits pathogens that may cause diseases it might carry. Fleas smell exhaled carbon dioxide from humans and animals and jump rapidly to the source to feed on the newly found host. The flea is wingless so it can not fly, but it can jump long distances with the help of small, powerful legs. A flea's leg consists of four parts: the part that is closest to the body is the coxa; next are the femur, tibia, and tarsus. A flea can use its legs to jump up to 200 times its own body length (about ).