There were a couple of things about Body Snatchers (I always hated the spelling 'Snatchas', which Chris Clark insisted upon in order to avoid potential copyright claims) that made it unusual. Firstly it was frame-locked, not an easy thing to accomplish with the hardware available, and secondly all the objects existed independently of the display limitations, so an alien that was off-screen could shoot at you, and you could shoot at it. This was something that was generally true of Design Design games. Note that Body Snatchers was a Design-Design game that was marketed by Crystal Computing.
In order to achieve frame-rate there were some fairly aggressive programming strategies. The objects were drawn using code-fragments rather than having character drawing routines and graphical data, there was some hideous code to undraw objects that used the stack pointer to build a definition of what was displayed on-screen, since there was nowhere near enough time to just clear the whole frame-buffer.
To minimize colour flickering most objects were drawn on 8x8 pixel boundaries and moved in multiples of 8 pixels, this being the minimum size of cell that could be assigned different colours with that display technology, and so objects moved very quickly indeed at 50*8 pixels per second...
There is a cheat code (long forgotten) that puts the game into a mode where the players ship repeatedly explodes, and during some television coverage of a computer trade-fair they used our stand as the backdrop for the report, probably the first time a Design Design game appeared on national television (quite possibly the last time as well, now I come to think of it) and this was what was running on the computer that the reporter was sitting in front of. At the end of the report he turned to the computer and pretended to play the game for a few seconds, which looked pretty silly with the ship doing nothing but exploding... Various members of Crystal Computing were visible in the background during this coverage, vying to be seen on national television; all except the programmers, of course, who were off boozing in the bar. That being the only thing worth doing at trade-fairs...
The game was credited to Neil and I, but in practice Neil had very little to do with the game and provided support on the development tool side of things; I suspect Neil would have contributed far more if the game hadn't been so boring, from what I remember of the whole process he really wasn't interested in writing arcade clones. I don't blame him, I pretty well lost interest after I'd proved to my own satisfaction that it could be done at frame-rate, which shows in the game itself - there's very little to recommend it. (Many years later I wrote a follow-up for the PC more or less as an apology for making such a pigs-ear of Body Snatchers).
There are several jokes in the high-scores, some of which have been detailed elsewhere and some of which are sufficiently obscure that they are mercifully lost to time. One that I remember fondly and which I believe has escaped documentation until now is the way the lengths of the lines of text in the high-score table were chosen so that the outline of the right-hand side forms a profile view of Graham's head (Graham Stafford was a founder member of Crystal Computing). He, I think it is fair to say, had a prominent nose, to which the term beak-like could easily be applied. As well as caricaturing the outline I was particularly proud of working the word "eye" into the high-score table entries (song lyrics) about where his eye should be... I don't think I ever pointed this joke out to him, and but for the fact I'm twiddling my thumbs writing this while a huge file downloads it would certainly have been forgotten. Ho hum, as Martin Horsley used to say.
What else? Um... The 'men' that the aliens are abducting, and which you have to rescue, are clearly depicted wearing skirts. There is a reason for this - they're women. This was a joke, something along the lines of me not wanting to write a game were you fly round picking up men. Laugh? We nearly did... There was a follow-on joke about there being bonus extra people because of what the women you saved got up to between the sheets, but it's best forgotten. I was a callow and inexperienced youth, such was my sense of humour back then.