When told during the investigation into her dead grandson's death that his body had marks on it made by an adult's teeth, Donna Parangi immediately offered her own set for examination, a court has heard.
She did this during a recorded interview with a detective more than four months after Isaiah Te Rangi was pronounced dead at his family's Ruatoki home on November 2, 2015.
The Crown says Isaiah died when he overheated after being left for at least three hours inside a car with the windows up, while his mother Lacey Te Whetu and Parangi, 48, binged on synthetic cannabis.
Parangi is on trial for manslaughter in the High Court at Rotorua, accused of depriving the eight-month-old of the necessaries of life and failing to reasonably protect him.
She denies the charges.
In the police interview played to the jury on Thursday, Whakatane Detective Michael Hayward described the teeth marks as the "horrible bit" of a pathology finding into baby Isaiah's death.
He also told Parangi that bruises found on Isaiah's body were caused by a blunt force impact, however his death had been due to over-heating.
"I want to know how the hell they [bruises] happened, how they got there" Parangi demanded in the interview.
She said she had changed Isaiah that morning and there had been no bruises on him, "just a nick by his ear where he'd scratched himself".
Parangi also repeatedly told the detective she had agreed to leave Isaiah to sleep in the family's station wagon, but that she had ensured he had ventilation.
"I left the windows down, the doors and sun roof open," she insisted.
Shown a photograph of the vehicle where police found it parked, she was adamant it had been moved from the shaded position she and her daughter left it in.
Questioned about her drug use, Parangi acknowledged she regularly smoked ''shop synnies" (synthetic cannabis) for relaxation, saying "it was not strong or anything".
She said she was able to do her housework like normal after she smoked the drug, saying" it didn't blow my mind or anything".
She also denied she had helped cover up the role her daughter Te Whetu played in Isaiah's death, while saying she had no time for Te Whetu's partner Shane Neil, who she claimed suffered mental health issues.
Te Whetu and Neil have pleaded guilty to the infant's manslaughter.
The trial resumes on Friday.