The Vow viewers were left sickened at gruesome scenes which saw the leader of the NXIVM sex cult's initials branded into women's skin.
The HBO documentary series follows the story of the NXIVM group, which made headlines last year when some of its famous members faced charges of sex trafficking, racketeering and forced labour.
NXIVM was also accused of keeping sex slaves and branding its members with leader Keith Raniere's initials, which was explored in last night's episode.
Raniere was found guilty of racketeering, sex trafficking, forced labour conspiracy and wire fraud conspiracy earlier this year.
The gory scenes left viewers horrified, with one tweeting: "I’m not going to lie, at first I kind of understood how these people could be tricked into accidentally joining a cult.
"But master/slave relationship? Branding? Collateral? Penance? How were these women not running for the hills?"
Another posted: "Grandmasters, masters, slaves... and this lady said 'she is in'? And she does a nude photo? Gets branded?! WHAT IS HAPPENING?!"
A third wrote: "By ep 2 they're starving all the women and forcing them to be branded. At what point do you not realize you're in a cult?"
Another agreed: "Wowwww they really branded these women. I mean you hear it but when you see it."
Membership of NXIVM reportedly included Hollywood actresses, heiresses and even the son of a former Mexican president.
Over the last few months shocking details about the cult have emerged.
There were allegedly naked meetings where only the cult's "slave master" could be clothed.
The "slaves" were restricted to diets of only a few hundred calories a day.
Members of the group were branded with Raniere's initials using a cauterising pen, often on their pelvic areas, in ceremonies which were filmed by members.
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