Kimberly Bell, a former mistress of San Francisco Giant slugger Barry Bonds, leaves the Phillip Burton Federal Building in San Francisco, California March 28, 2011. Bell said in court on Monday that the baseball star's testicles changed shape and he often became enraged with her, which prosecutors say is evidence that Bond used steroids.

*Barry Bonds’ former mistress Kimberly Bell was called to the stand of his perjury trial on Monday, offering explicit testimony about her relationship with the baseball player and the various physical and psychological changes she witnessed in him – which she attributes to the use of steroids.

Bell testified that Bonds blamed a 1999 elbow injury on steroid use, and that the body and behavior of the home run king changed during their nine-year relationship.

Bonds threatened “to cut my head off and leave me in a ditch,” she said. “More than once.”

She said Bonds told her “he would cut out my breast implants because he paid for them.”

As for the Arizona house he had helped pay for, “he told me he would burn it down.”

She also discussed how Bonds became verbally abusive and said that his physique changed, offering a lurid description of his shrinking testicles, back acne, scalp hair that fell out and chest hair that turned gray. Such mental and physical symptoms are associated with steroid use.

Bonds goes through security at a federal courthouse as his trial resumes, Monday, March 28, 2011, in San Francisco.

Prosecutors allege Bonds lied when he told a federal grand jury in 2003 that he never knowingly used performance-enhancing drugs.

Bell met Bonds in 1994 and testified that from 1999 to 2001, “he was just increasingly aggressive, irritable, agitated, very impatient.”

In testimony similar to that of former Bonds business partner Steve Hoskins last week, she said that in at least two different years at spring training, she saw Bonds and personal trainer Greg Anderson “go into a bedroom off the kitchen and close and lock the door.”

She said Anderson “would always have a little satchel with him.” She saw those scenes played out multiple times.

Prosecutors claim Anderson, who has been jailed for refusing to testify, repeatedly injected Bonds with performance-enhancing drugs.

Cristina Arguedas, one of Barry Bonds' attorneys, arrives at a federal courthouse for Bonds' trial, Monday, March 28, 2011, in San Francisco.

Bell was then cross-examined by Cristina Aguedas (seen above), who attempted to paint the witness as a scorned  ex-lover, gold digger, liar and the instigator of a mortgage fraud scheme.

Arguedas attacked Bell’s motives for trying to write a book about Bonds, and suggested Bell grew increasingly resentful over the course of the relationship as Bonds got married to another woman and pushed Bell to the side.

Arguedas concluded by getting Bell to admit that some statements she made to Playboy and the grand jury about changes to Bonds’ sexual organs were overblown.

Today, it’s expected that former baseball players Jason and Jeremy Giambi will be the first of several athletes called to testify, possibly as soon as Tuesday afternoon. The brothers have both admitted to using performance-enhancing drugs they obtained from Bonds’ personal trainer, Greg Anderson.

Federal prosecutors also are expecting to briefly question two witnesses who will testify to the “chain of custody” of Bonds’ Major League Baseball-mandated urine sample in 2003. Prosecutors allege that the sample tested positive for a designer steroid.

Former San Francisco Giants trainer Stan Conte also is slated to testify about Bonds before prosecutors turn their attention to the ball players.

Other athletes who are on the government’s witness list include several former teammates of Bonds: Armando Rios, Benito Santiago, Bobby Estalella and Marvin Benard.

In addition, former Oakland Athletic Randy Velarde is scheduled to testify immediately after the Giambis. All the players except Jason Giambi, who is with the Colorado Rockies, have retired.

All the players will testify about their ties to Anderson, who is in jail on contempt of court charges for refusing to testify at the trial.