As if the idea of Negan wearing a Whisperer skin mask wasn’t scary enough, actor Jefferey Dean Morgan revealed what he secretly did to make the sight even creepier.“I went to [special effects artist] Greg Nicotero when mask was being built...and had one ask,” recalled Morgan in a tweet. “Was there a way to cut a smile into it? No other mask has one. Greg being Greg...thought it was a great idea, VERY negan. And did it. HENCE it being the coolest.”RELATED: The Walking Dead Midseason Return: Carol Learns A Lesson At A Terrible Cost

The Walking Dead’s tenth season has seen Negan join up with Alpha and her gang of Whisperers following his escape from Alexandria. He has been trying to gain the trust of Alpha and her followers, and one way includes donning the fleshy skin and sleeping with Alpha. The shocking moment came during Season 10’s midseason premiere.

Morgan described what it was like filming the sex scene, and more specifically, kissing a Whisperer mask, on Twitter Monday.

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“It smells. Not cuz of Sam, she smells delightful,” Morgan said of his Walking Dead co-star Samantha Morton, who plays Alpha. “Crud they are made of, smells...decidedly not delightful,” Morgan explained. “Lips don’t even touch, its mask all the time. Not to take the romance out of the moment...but it ain’t even a tiny bit that. Plus we were laughing at the absurdity.”

The Walking Dead stars Norman Reedus, Danai Gurira, Melissa McBride, Josh McDermitt, Christian Serratos, Jeffrey Dean Morgan, Seth Gilliam, Ross Marquand, Khary Payton, Cooper Andrews and Samantha Morton. It airs Sundays at 9 p.m. ET/PT on AMC.