Strychnine
In the past, many of the rat poisons contained strychnine. I don’t know if it is still legal to bring strychnine into Guyana to be used in rat bait. It was effective in the past, so I do believe that, in spite of the success of newer rat poisons, strychnine might be available for use (and misuse and abuse) as a rodenticide.
In order to entice the rats to eat the poison, pellets are produced with strychnine and then alluringly coated in attractive colours.