Updated! New pics from the Black Cat cake The Beast (scroll down).

I had a dud cake I was taking apart, so I decided to take a few pics to show what's inside them.

Under the wrapper the tubes are glued and wired (the wire and two rows of tubes have been removed)

Pulled apart with fuses linking them

the shell from one tube

Lift charge and shell. Notice the solid powder delay on a plastc endplug rather than time fuse.

The contents of the shell (which included 4 firecrackers)

I had one of these that I bought and after I saw one in action decided it wasn't that great and might look cooler if turned into a mine. The effect is a shell with a spark tail is launched, when it gets to a certain height it turns to a helicopter, then shoots a few stars.

The cake:

Under the label:

The tubes apart:

Left to right - Tube, lift charge, shell:

Inside the shell:

Better shot of inside shell - Black end is lit by lift charge, orange clay has hole with powder that creates spark tail, burning white powder pushes through hole creating spinner effect and then ignites the stars: