Didn't he show his real penis in Monday though? He's pretty big. Plus this was said in an interview, "According to a recent GQ UK interview with special effects makeup artist Jason Collins, the talking penis was made from an actual cast of Sebastian Stan's junk."
"It was made from silicone and involved lifecasting Sebastian so that we could then sculpt the appropriate size and blend points," Collins told the magazine. "Once we were done sculpting, another mold was made and we cast it from a plasticized silicone. The silicone is medical grade and gives the appendage a life-like fleshy quality."