One of the paintings hanging in Ethel Cripps' apartment is The Dream by Pablo Picasso.
As Dream stretches down into the water, after sprinkling the Sand acquired at Cain and Abel's, a black silhouette with shining white eyes forms within his reflection. Immediately after, a bone-white arm reaches up and grabs his arm, dragging him down. This figure is a comics-accurate depiction of Dream, as illustrated in the DC Vertigo Series.
The filming location for Cain and Abel's Houses of Mystery and of Secrets was Scotney Castle, near Lamberhurst in Kent. Whilst some distinctive parts of the houses were filmed, there is also a lot of CGI to make both look larger.
The car driven by Johanna Constantine is a Ford Sierra RS500 Cosworth. As only 500 were ever built, it is quite appropriately regarded as a "dream car" by many of those familiar with its motorsport heritage.