Zack Snyder's latest release tells the story of a group of young women who live in a mental asylum, and who have their world turned upside down by the arrival of a new inmate.
"Sucker punch is this idea of taking an unexpected blow," Cornish explained to MTV News. "A lot of the girls are totally unprepared for what's about to happen to them."
The actress explained that the arrival of Baby Doll, played by Emily Browning, changes the character's lives forever.
"[Baby Doll] changes their whole perception of freedom, of hope, of escapism," Cornish continued. "And so their ways of life are challenged, they're sucker-punched with this whole idea of freedom."
Co-star Carla Gugino agreed with Cornish's description of the film, claiming that it embodies its title by being something that "hits you in the gut".
Cornish recently said that she was surprised by how much she enjoyed being allowed to fire a gun and take part in fight scenes during the filming process.
Sucker Punch was released in US cinemas this weekend, and debuts in the UK on Friday.