An Indian-origin computer engineer has been jailed for nine years by a British court for fracturing his girlfirend's four-year-old son's skull.
Vishar Jain also hit his victim's mother when she tried to intervene, Birmingham Crown Court was told during a hearing.
The boy's mother, with whom Jain had been in a relationship for two years, suffered cuts and bruises to her face.
Judge Philip Parker described the attack as an "unexplained outburst of uncontrollable violence" while sentencing the 44-year-old this week.
Jain, who had earlier admitted causing grievous bodily harm with intent and common assault, rained blows and kicks as he sat on a sofa with the child and his mother while watching television.
"You became irritated by his behaviour when he was sitting between you and his mother," Judge Parker told Jain in his ruling.
"You chastised him and then what followed was a quite unexplained outburst of uncontrollable violence which was your reaction to no more than the child simply sighing."
According to media reports, the boy was twice thrown to the wooden floor and stamped on, and spent two weeks in intensive care in hospital recovering from his injuries.
He suffered a fractured collarbone, cuts to his mouth and multiple bruising, sustained when he was repeatedly punched and kicked, the Birmingham Mail reported.
Prosecutor Claire Harris told the court that the boy said something that Jain interpreted as interrupting the adults' conversation.
He slapped the child on his face and when his mother tried to intervene he slapped and punched her. "He then lifted him up into the air and dropped him on the floor," she said.
The boy was so traumatised by the attack that he reportedly suffered nightmares and would lapse into zombie-like trances.
The court heard there was a "significant risk" Jain would behave in a totally unjustified and irrational way again.
Following the case, Hayley Bubb from Birmingham's Child Protection Team said: "We will never know why Jain decided to viciously beat this little boy.
"This was an unprovoked and sustained attack on a defenceless child, which he has never explained. Although he has recovered well, physically, from his injuries, emotionally it will take a long time for him to get over the attack.
