Dale removes several paintings from the wall. Then, when Tracy enters, she admires the paintings still on the wall, including two of the paintings that Dale had taken down already.
When Tracy leaves the mansion, she pushes open the sliding door that had been scratched to look as if it was jimmied open and leaves it wide open. Moments later, the security guard explores that direction, and the sliding doors are once again closed.
While in the TV studio, Columbo asks Dale if the coffee machine works, and Dale confirms it does. After Columbo puts coins in the coffee machine, he instantly removes the cup of coffee from the machine (which should have taken some time for the machine to fill). Columbo waves his (right) hand holding the coffee around as if the cup were empty while talking to Dale. Then the cup disappears, only to reappear, when Columbo puts the cup on a table, having never once taken a sip of coffee.
When Columbo sets down his coffee cup and unrolls the painting of the blue horse, he holds the painting open with both hands, left hand holding his cigar. Camera changes to a shot of the painting from Columbo's perspective, now held only with his right hand, left hand gone. When the scene reverts to the previous camera, both hands again hold the painting, but now his cigar has impossibly transferred to his right hand. Also, the coffee cup which Columbo set on the table has moved, now twice as far from the edge as where Columbo placed it.
While in the TV studio, after having his makeup removed, Kingston buttons his shirt collar and adjusts his tie. A few seconds later, he again buttons his shirt collar and arranges his tie.
In Prescription: Murder (1968), the reception room of Dr. Fleming's office features a distinctive painting (trees and white houses with red roofs) which is shown in several scenes. The same painting appears in this show as part of the art collection sliced and stolen by Dale Kingston.
When Dale sits for makeup removal, his elbow collides against Columbo's cigar, end on, revealing that the cigar is unlit. When the camera changes from the two-shot to a wide shot, smoke reveals that the cigar is lit. It's also clear it left no mark on Dale's white striped dress shirt.
(at around 25 mins) When Columbo questions the painter Sam, the model obviously doesn't look anything like the woman Sam's painting; even her pose is completely different.
(at around 5mins) When Dale Kingston answers the door, the shadow of the boom microphone can be seen moving on the door.
At 5 min 30 secs, when Dale Kingston answers the door, the shadow of the boom microphone moves on the door.
When Dale Kingston is on TV lecturing about Goya, Kingston compliments him by saying he was the "penultimate artist". The word "penultimate" means "next to the last", so the word makes no sense in the script. "Penultimate" is commonly misused in place of "quintessential", mainly due to its relationship to "ultimate". Some people believe it to be a fancy way of saying "better than ultimate", simply due to the way it sounds.
Shortly after Dale Kingston (Ross Martin) arrives at the murder scene, a police officer tells him they haven't been allowed to check for fingerprints on any of the canvases. He says that it is okay "as long as you're careful". In fact, it definitely would not be okay. Fingerprint powders are notorious for penetrating surfaces and very difficult to clean off. Using them on any piece of art canvas would destroy its value. Even dusting for prints on the frames would endanger the piece with powder spill. Kingston should have been aware of this.
2:40 into the show, as Dean is ransacking to make the murder scene look like a theft, he flips a chair, approaches a painting, tilts it off center and moves on while behind him as he steps away to continue his ransacking the painting returns to its original position centered right side up.