Really enjoyed seeing CALTIKI IL MOSTRO IMMORTALE on the Arrow Blu-ray. It comes with two excellent commentaries by Mario Bava experts Tim Lucas and Troy Howarth. Bava shot the film and did the special effects, and directed a big chunk of it also.
Unusually for a total B-picture, the film is so full of stuff that the commentaries can’t cover it all. Lucas tells us that director Riccardo Freda himself scultped the statue we see in the niche in the cave with the pool from which monster tripe-blob emerges.

So I became really interested in the wide shot, in which the camera tracks back and pans left as the protags descend the stairs into the cavern, and the statue is revealed. A miniature statue standing in a full-sized location.
It’s clear from the close-up that the statue is quite small, just like the bronze Brian Blessed at the start of Branagh’s HAMLET (a lesser film than CALTIKI): if it were as big as it appears, its surroundings would be better focused. For all his wizardry, Bava wasn’t always able to solve this issue — I regard with affection the heroes’ spaceship in PLANET OF THE VAMPIRES, bits of which are nearly always out of focus, proving that it’s a tiny model.
The way to do this usually is to suspend the miniature in front of the lens, close to it. If everything is successfully in focus, the miniature can be made to appear as if it’s enormous, sitting in the background, instead of small and hanging in the foreground.
You can even pan, since the foreground miniature (or glass painting) will move through frame at the same rate as the background.
The complication here is that the camera is also dollying backwards, but they try to time it so that the camera’s motion is over just as the statue comes into view.
And they don’t quite manage it, with the result that the statue appears to float backwards into its niche just as it appears — oh just the tiniest smidge. The conviction added by the camera movement is well worth the slight flaw of the statue’s drift. Guaranteed most viewers assume the statue is life-sized.

Two more thoughts — the serpent and skull cutaway suggests that Freda or Bava or one or writer Filippo Sanjust may have seen THE BLUE LAGOON, the film that terrified a young David Cronenberg with its image of a skull rising up on the end of a snake; and I believe Lucas, whose exhaustive analysis of the film’s beautiful glass shots is fascinating, may be wrong in assuming the volcano effect, made using a fish tank, must have been shot upside-down. It MAY have been. But the “lava” squirts up from below, then descends in your basic DEATHLY PALL, which would also be consistent with the fluid (Lucas suggests a lead suspension, but ordinary paint and milk seem possible) being pumped upwards from below and then curling down when it hits (offscreen) the top of the water. I think this is likelier because it’s simpler. While one way to pull off a trick is to put more effort into it than anyone would think likely, Bava special effects are often distinguished by simplicity and boldness combined with tremendous skill and imagination. Such may be the case here.