As previously established, Black Widow’s opening credits sequence offers a glimpse into how Natasha Romanoff and other young girls like her are made into Widows.
As Yelena Belova points out to her adoptive sister at one point, she and other were not manipulated psychologically, but surgically.
The credits present close-ups of the young Widows being prepped for what is essentially a lobotomy that can only be reversed with an antidote that cures Yelena while she is on a mission to repossess it.
Indeed, this is easily the most horrifying moment in already thoroughly depressing sequence.