Pay It Forward

When Trevor McKinney (Haley Joel Osment) begins seventh grade in Las Vegas, Nevada, his social studies teacher Eugene Simonet (Kevin Spacey) gives the class an assignment to devise and put into action a plan that will change the world for the better. Trevor's plan is a charitable program based on the networking of good deeds. He calls his plan "pay it forward", which means the recipient of a favor does a favor for three others rather than paying the favor back. However, it needs to be a major favor that the recipient cannot complete themselves.
Trevor does a favor for three people, asking each of them to "pay the favor forward" by doing favors for three other people, and so on, along a branching tree of good deeds. His first good deed is to let a homeless man named Jerry (Jim Caviezel) live in his garage, and Jerry pays the favor forward by doing car repairs for Trevor's mother. Trevor's efforts appear to fail when Jerry relapses into drug addiction, but Jerry pays his debt forward later by talking to a suicidal woman, who is about to jump off the bridge.
Meanwhile, Trevor's mother Arlene (Helen Hunt) confronts Eugene about Trevor's project after discovering Jerry in their house. Trevor then selects Eugene as his next "pay it forward" target and tricks Eugene and Arlene into a romantic dinner date. This also appears to fail until Trevor and Arlene argue about her love for Ricky, her alcoholic ex-husband, and she slaps him in a fit of anger. The two adults are brought together again when Trevor runs away from home and Arlene asks Eugene to help her find him.
After finding Trevor, Arlene begins to pursue Eugene sexually. Eugene has deep burn marks visible on his neck and face, and he initially resists Arlene's overtures out of insecurity. When they finally sleep together, he is seen to have extensive scarring all over his torso. Arlene accepts Eugene's physical disfigurement and forms an emotional bond with him, but quickly abandons their relationship when Ricky (Jon Bon Jovi) returns to her, claiming to have given up drinking. Ricky's return and Arlene's acceptance of it angers Eugene, whose own mother had a habit of taking his abusive, alcoholic father back. When Arlene attempts to explain to Eugene that she believes Ricky has changed for good, Eugene explains that his father intentionally burned him by knocking him unconscious, then pouring gasoline over him and igniting it. He berates Arlene for being "one of those women" and warns her of Ricky's potential to abuse Trevor. When Ricky drinks again and resumes his abusive behavior, Arlene realizes her mistake and forces him to leave.
Trevor's school assignment marks the beginning of the story's chronology, but the opening scene in the film shows one of latter favors in the "pay it forward" tree, in which a man gives a car to Los Angeles journalist Chris Chandler (Jay Mohr). As the film proceeds, Chris traces the chain of favors back to its origin as Trevor's school project. After her date with Eugene, Arlene paid Jerry's favor forward by forgiving her own mother, Grace (Angie Dickinson), for her mistakes in raising Arlene, and Grace, who is homeless, helps a gangmember escape from the police. The gang member then saves a girl's life in a hospital, and the girl's father gives Chris his new car.
Chris finally identifies Trevor as the originator of "pay it forward" and conducts a recorded interview in which Trevor describes his hopes and concerns for the project. Eugene, hearing Trevor's words, realizes that he and Arlene should be together. As Eugene and Arlene reconcile with an embrace, Trevor notices his friend Adam being bullied by gangster-like children, as he has several times before. He pays it forward to Adam by rushing into the scene and fighting the bullies while Eugene and Arlene rush to stop him. When one of the bullies takes a switchblade out of his pocket, Trevor is stabbed in the abdomen and dies from his injuries. This news is reported on television; Arlene and Eugene are soon visited by hundreds of people who have participated in or heard of the "Pay It Forward" movement by gathering in a vigil to pay Trevor their respects.

Question: Who warns Arlene of Ricky's potential for abuse?
Answer: Eugene