Goofs

The flowers on the hearse move from being on top of the car to the ground, as too the position of the two policemen is not the same.

When Det. Inspector Matthews goes to arrest Lowis at his home, he goes into the kitchen. From the inside there are curtains on the window and door, and bright lights streaming in from outside. But, in the next shot, the layout is completely different - the curtains are gone and it's dark outside.

Insp. Matthews tells Edgar Lowis that his 'dabs' (fingerprints) were found on eggshells found in the getaway car. Lifting fingerprints from eggshells was not possible in 1970. The technique was only discovered in 2015.

Be that as it may, Edgar isn't the smartest crook. Matthews was bluffing him about getting prints from the eggshells.

There is a clear overdub when Wolfe and Venetia arrive at the country house for the party. As they are walking up the drive they both survey the front of the mansion. Wolfe describes the house as, "fit for a king". Venetia responds, "I bet the bathrooms are freezing", but if you watch her mouth movements closely, she actually completes Wolfe's sentence with the phrase , "or queen" .