Barnaby is unhappy with Jones for providing Barnaby's mobile number to Chief Superintendent Cotton. But in a prior episode, "Days of Misrule," Barnaby receives a mobile call from Cotton (with the display name "Wonderboy").
Jones receives a scratch on his face while tearing through the forest after the suspect; however, during the autopsy in a previous scene, he already had the bloody scratch on his face.
Whilst being questioned in his empty house, Drinkwater says that Kingslake hit his ball into the trees on Crisp's Folly. The ball had actually landed on or near the fairway, not in the woods at all. The killer swipes it into the woods and then through it at Kingslake, hitting him in the forehead.
As the person that finds the second murdered body, and being left-handed himself (but plays golf right-handed), Jones would have intuitively recognised from the blood stains on the victim's shirt that the murderer was also left-handed.
Being a minority group, left-handers have an affinity with one another even if they have nothing else in common.
At one point a little over halfway through the episode, Barnaby and Jones are seen walking outside the golf club buildings. A British flag is shown in the background flying upside down.
On the board with the map detailing the golf course, there is a handwritten note that says "Victim found by DCI Jones". Indeed, the body was found by 'DS Ben Jones', but Jones is a detective sergeant, not a detective chief inspector.