While there was always a possibility that Jodi Arias could take the stand in her own defense, those following her capital murder trial in Phoenix were stunned Monday afternoon when that possibility came true.

With her hair pulled half-up, clad in khakis, a black t-shirt and glasses, Arias spoke directly to the jury when she answered why she killed her ex-boyfriend, Travis Alexander: “The simple answer is he attacked me and I defended myself.”

During her first day of testimony, Arias recalled her childhood and the alleged physical abuse she claimed she suffered at the hands of her own parents.

That testimony sparked a debate Tuesday morning on “Good Morning America” between HLN’s Nancy Grace and ABC’s Dan Abrams about Arias’ demeanor and credibility on the stand.

“She’s a great liar, but she’s a great witness,” Abrams said.

“You’re under her spell,” Grace fired back.

“A mannequin at Saks Fifth Avenue had more life and feeling,” she added.

The Orlando Sentinel reports laughter broke out in the studio when Abrams responded to Grace’s comment, saying “I am…I could have been her next victim.”

Jodi Arias will be back on the stand Tuesday afternoon. Live coverage of her testimony begins at 12:30 p.m. ET on HLN.