In the world of “Walking Dead,” an even bigger threat than the zombies is whether or not Norman Reedus has brushed his teeth.

The actor, famous for playing the crossbow-wielding Daryl Dixon, is also known for licking castmates, fans, monuments and pretty much everything he can. At this point, his name has even become a term on Urban Dictionary for licking someone’s face.

On Tuesday, Reedus finally explained to Conan O’Brien how it all got started. He also recalled a weird fan experience involving rubber horse heads that amazingly makes licking seem pretty normal.

“The Walking Dead” airs Sunday at 9:00 p.m. ET on AMC.