Images of the men come from a documentary, "The Jihadis Next Door," which airs Tuesday on Britain's Channel 4 station.
The men — Mohammed Shamsuddin and Abu Haleema — were associates of Siddhartha Dhar, a former bouncy castle salesman believed to be a masked militant in a recent ISIS execution video.
“It’s a horrible way to die,” Shamsuddin said while watching the video, chuckling, according to The Sun. “This guy is foaming at his mouth, you know what I mean. Wow.”
Filming for the documentary occurred during the past two years, before Dhar fled to Syria.
"One day, when the Sharia comes, you'll see this black flag everywhere," Dhar says in a video clip from the documentary.
After the ISIS execution video emerged, documentary director Jamie Roberts received a text message from one of the activists he had filmed, he told International Business Times.
"You may know the voice," the activist texted to Roberts.
Roberts told the news publication that Dhar was one of the "dullest and most one-dimensional" of his documentary subjects.