A keeper holds the head of JF, a 4.6 metre (15 feet) long reticulated Python ahead of a health check and ultrasound heart scan at Chester Zoo in Chester, northern England September 5, 2012. The zoo's two reticulated pythons are taking part in cardiological study as part of a joint research programme between the zoo and Cardiff Metroploitan University. REUTERS/Phil Noble (BRITAIN - Tags: ENVIRONMENT ANIMALS SCIENCE TECHNOLOGY HEALTH)