Yep, the other explanations such as heavy-metal poisoning from zinc contaminated rats are likely to produce illness or other changes in behaviour prior to death. A rat eats loose zinc on the mesh of its enclosure and may be fed off before suffering the effects itself, but the end-user, the snake, may have it in their gut for some time. I doubt that zinc would be bright & shiny after the process anyway, definitely not glittery, if my school experiment memories of using zinc & HCl to produce hydrogen hold true.
Jamie