What is the reason so many poisonings go undetected at first?

Poisonings mostly have no taste or smell. Thallium is one of the poisons that are hard to detect. Most of these poisons are always prescribed to many patients and can be misused. We also have to take into consideration thay poisoning attacks our immune system and internal organs. Side effects of poisoning are flue like. So when the individual is feeling ill. nobody is going to think it’s poison at first until about 30 mins to an hour. that’s why it takes so long to be undetected at first. because of the symptoms, smell, taste it can really be easy to poison someone