- "Bliss is a sickness! It's mind control!
Bliss is a feeling of euphoria provided by Anna (or any mature queen) to the Visitors to keep them under her control and united as a species. It is not clear whether it is a purely telepathic or purely technological phenomenon, though Visitor technology has been shown to be able to manipulate the mind before (interrogation technology, etc.).
The bliss is achieved by Anna standing naked in a special room on her mothership (surrounded by what seems to be the technology that transmits the effect and telepathically projects euphoria into the minds of very Visitor on Earth along with a physical visage of herself. The euphoric effect is accompanied by Anna's voice saying encouraging things making the Visitors feel safe and protected from harm, believing Anna will always protect them. The bliss also keeps the Visitors from embracing emotion and making the Visitors dependent on Anna to achieve happiness and become highly devoted to her, worshiping her as a goddess and even becoming willing to die for her.
According to Ryan, the effect of the Bliss is essentially a drug that Anna uses to control the Visitors, leaving her followers as no better than junkies looking for another fix. Although never stated explicitly, it appears that a Visitor's resistance to Bliss is tied to the level of human emotion they have embraced, and that those who have embraced human emotion (usually members of the Fifth Column) are more resistant or even immune. A Fifth Columnist revealed his immunity to Bliss by detonating a grenade while the other Visitors on his ship were caught in the projection. Later on, Joshua and Lisa, the former a Fifth Columnist and the latter having embraced human emotions, also displayed total immunity to Bliss, even though they were on the same ship as Anna. After Ryan, a vocal proponent of embracing emotion, was separated from his girlfriend, Valerie Stevens, he was halfway to being affected by the Bliss, but managed to snap himself out of it. His disillusionment and disappointment after her departure may have broken down his resistance to Bliss.
In "Red Sky", Anna appears entrap Ryan in her Bliss outside of her special chamber, suggesting that the Bliss might be a telepathic or pheromone-based phenomenon she produces herself, with the chamber simply projecting it across the Visitors as a whole.
Some time later, Anna gives Amy a condition that causes her pain which only bliss can alleviate. She uses this as leverage against Ryan, withholding bliss from his daughter if he does not cooperate with her orders. As a result of Joshua's accelerated growth experiments, however, Amy eventually becomes immune.
When Lisa brings Ryan to see Diana and informs the former queen of his hybrid daughter's dependence on Bliss, she offers to use her own bliss to cure his daughter, suggesting that bliss can be produced by any mature Visitor Queen. ("Uneasy Lies the Head") Lisa later confirms that it is an ability all queens possess.("Devil in a Blue Dress")
During the early days of the Visitors' infiltration of Earth, Diana experimented with blissing humans, but was unsuccessful. Anna, in defiance of Marcus's warnings, later attempted this herself. Through tremendous effort, Anna appears to be able to bliss one human at a time, but the process nearly killed her both times.("Devil in a Blue Dress"). Later, Anna tries to bliss the entire human population.
Bizarrely, Amy seems to also be capable of generating bliss, and assists Anna in projecting it to the human population.("Mother's Day") Since her father is a Visitor, this suggests the ability to Bliss is carried through the male as well the female line even if the males are incapable of performing it. It is not clear if this means that Amy has any of the other abilities of a queen.