diet coke uses aspartame as a sweetener - in rat studies shows significant increase in brain cancer
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1392232/ (the UK paper which goes into it- but done in Italy)
of course, in the USA, the initial controversy was re-examined and downplayed, and aspartame ended up being labelled safe
(personally, I'd rather be on the safe side in case I drank a lot of diet coke)
I do love mods on knives - I'll post some of mine when I manage to get some time to take pics