Anyone who has a pet dog knows that they are pretty good judges of character – and black labrador Killian proved to be the best judge of all.
For the usually mild-mannered family pet took such a dislike to a couple's babysitter for their seven-month-old baby that he would go into a frenzy of aggression when she came to the door.
And pretty soon, parents Benjamin and Hope Jordan started to wonder why.
It was only after they spied on 22-year-old Alexis Khan that they discovered the truth: the sitter had been hitting their baby Finn.
The couple had hired Khan to babysit Finn when they first moved to Charleston, South Carolina last year. She cleared a background check and the two felt she was a 'good fit' at the time.
"About five months into her being our baby sitter, we started to notice that our dog was very protective of our son when she would come in the door," dad Benjamin told WCSC.
"He was very aggressive towards her and a few times we actually had to physically restrain our dog from going towards her."
The couple started to worry about their dog's behaviour, so one day they left an iPhone underneath the couch to record what happened while they were out.
When the returned home they sat down to listen, and what they heard was startling.
As Finn cried, Khan cursed at him saying: "Shut up. Shut the f*** up. Shut up."
And then there was slapping noises and Finn's cry for attention turned to a cry of pain.
"I just wanted to reach through the audio tape, go back in time and just grab him up," said Benjamin.
"To know that five months ago I had handed my child to a monster, not knowing what was going on in my house for that day."
He said that without the dog, they may never have found out about the abuse.
"Had our dog not alerted us to the trouble, had my wife's instincts not said we need to make something happen, it could have been Finn that was killed by the babysitter. You never know," he added.
The babysitter plead guilty in court to charges of assault and battery.
She will have to serve at lease one year of her three year sentence and register as a child abuser which will keep her from working with children in the future.