Ever wondered how idols manage to break out those perfect smiles in all those pretty group photos? 

Well, for veteran idol group Shinhwa, it's long since been a tradition for them to reach their hands over and grab one another's butts!

The group appeared on 'Weekly Idol' on January 18 and spilled all about their "tradition". First, MC Jung Hyung Don asked what Shinhwa actually do when taking photos, and Junjin took it upon himself to demonstrate for Jung Hyung Don. 

Next, the members made some suggestions on who has the best butt currently, from Minwoo, to Junjin with his ability to pop his butt, and more! 

Finally, the group all stood up with their backs turned to the camera, to physically and literally demonstrate how the whole butt-grabbing "tradition" works! You can imagine how full of smiles and laughs a photoshoot set might be, with such a fun "tradition" in play. 

SEE ALSO: Young K reveals JYP debuted DAY6 as a band because the members couldn't dance