Lt. Mercil, who supervises the training division's use of force training, told jurors that a still-image of Chauvin kneeling on Floyd's neck is not a restraint taught to Minneapolis Police Department officers.
Officers kept restraining Mr Floyd - with Mr Chauvin kneeling on his neck, another kneeling on Mr Floyd's back and a third holding his feet - until the paramedics arrived, even after he became unresponsive, according to testimony and video footage.
The handcuffed 46-year-old Black man fell limp and stopped breathing during the May 2020 arrest.
Hall is seen as a potentially important witness for the defense of police officer Derek Chauvin, who was seen in a phone video kneeling on the neck of Floyd for more than nine minutes.
Mercil testified that in his experience, it takes less than 10 seconds for someone to be rendered unconscious with a neck restraint.
Chauvin, who is white, has pleaded not guilty to murder and manslaughter charges for Floyd's arrest on suspicion that Floyd had used a fake $20 bill to buy cigarettes at a store. The footage of the arrest prompted widespread outrage, setting off protests across the US and around the world.
Mercil testified that officers are trained to use a proportional amount of force and on how to properly use neck restraints, handcuffs and straps.
Mercil agreed that if an officer is placing body weight with the knee on a person's neck and back that it would decrease their ability to breathe.
Minneapolis Police Chief Medaria Arradondo on Monday told the jury that Chauvin's training required him to stop the restraint and provide first-aid treatment while waiting for an ambulance to arrive.
Mr Chauvin's defence team claims the officer did what he was trained to do, and that Mr Floyd's drug consumption and his underlying health conditions caused his death.
She told the jury that if officers can not find a pulse on a subject, they are taught to immediately begin CPR and to administer first aid if they encounter a medical emergency.
"Just because they're speaking doesn't mean they're breathing adequately", Mackenzie testified when a prosecutor asked if a person can speak if they cannot breath.
But Schleicher then asked: "If they're saying 'Get off him, you're killing him, ' should the officer also take that into account and consider whether their actions need to be reassessed?"
The first witness of the day was Sergeant Ker Yang, a crisis intervention training coordinator with the Minneapolis Police Department.
Before the jury was brought into the courtroom in the morning, Hennepin County District Judge Peter Cahill heard arguments on a request by a friend of Floyd to quash a prosecution subpoena for him to testify.
Body camera footage shows Hall sitting next to Floyd in the vehicle when police arrived.
On Tuesday, the lawyer for George Floyd's longtime friend Morries Lester Hall said he is pleading the Fifth, in fear of self-incrimination.
Schleicher showed a still image taken from bystander video of Chauvin with his knee on Floyd's neck - one that jurors have seen several times - and asked Mercil: "Is this a use of force?"
Floyd's girlfriend, Courteney Ross, testified last week that she and Floyd struggled with opioid addiction, and that she thought Hall sometimes illegally sold pills to Floyd. Even so, the judge said Hall should be able to testify on Floyd's condition in the vehicle and whether he fell asleep suddenly after possibly taking opioid pills.
Cahill decided that most questions Nelson wanted to ask could incriminate Hall.