...present to you today are some of the world's deadliest poisons.

It's kind of weird to actually say "the most deadly", since as far as I know dead IS dead, and there shouldn't be any way to take that to a whole new level.
Still, let's not think about it. (Oh, by the way, let me take a second of warning you against using these stuff for anything.)

1. Hemlock, Aconite, Belladonna and Mandrake

If you are a fan of books you probably know these as "classics". They were pretty popular in the old times, because they were actually used by doctors for headaches or calming seizures, so if you had them on you, you could easily say that you had big problems and needed them for medical reasons. 

Hemlock is a "peaceful" killer, it will slowly paralyze every single nerve you own, ending with the respiratory nerves. Of course they are probably not THAT big of a deal nowadays, since people can survive the poisoning by being put under artificial ventilation till it clears the system. 

Aconite comes from Monkshood, and has a whole bunch of different names to it. Since I'm not Severus Snape to give you guys a lecture on it, you might just want to look them up if you are interested. I think it will be enough for you guys to know that this particular poison will first cause severe vomiting and diarrhea, and also heart arrhythmia (irregular heartbeat). 

Belladonna was mostly used by women - first and foremost they actually rubbed it on their face so they would get some "blush" going on, thinking that men find that sexy. It was also used by witches as a hallucinogen, that made them feel like they could fly. They had to be pretty careful, tho, because even a single full leaf could cause extreme hallucinations and such a rapid pulse that they would more than likely end up having a heart attack in no time at all. 

Mandrake was most popular in Spain and Portugal. It will attack the liver and the kidneys. It's so potent that it's used to take off warts nowadays, and it usually comes with the warning of not exposing healthy skin to it. 

2. Botulinum toxin

Or botox, because most of you would recognize it that way better. Now, this particular... uhm... chemical, will block the nerves giving off signals to the brain, so that's actually how it works when people inject themselves with it to treat their wrinkles. It actually paralyzes the muscles in the face. Temporarily, of course. If someone would get botox poisoning, it would be pretty bad, since their nervous system would fail and they would die a horribly painful death. 

3. Ricin 

This is so potent that a dose of the size of a few grains of salt could already kill an adult. It causes nausea, diarrhea, tachycardia, hypotension, seizures, and in the end, if not treated, will most likely cause death via shock. It can take up to even a week of this before you would die. 

4. Sarin 

This is actually a colorless and odorless liquid, used as a chemical weapon. It resembles common insecticides, and it will also attack the nervous system. 

If a person comes in contact with it, his or her clothes will actually release sarin for an extra 30 minutes after the exposure - which can expose other people to it. If someone would ingest it, they would die in about a minute. 

Sarin is about 500 times more poisonous than cyanide. 

People usually die from asphyxiation because every single nerve shuts down in their body, but the whole thing will first start with runny nose, nausea and drooling, then comes the vomiting, diarrhea and  urinating, then come the seizures, all the while the victim suffocates. 

5. Compound 1080 

This is sold as a pesticide. 

Just...throwing that out there. 

Humans usually show symptoms after about 30 minutes or so if they are exposed to it. These usually include nausea, vomiting, abdominal pain, sweating, confusion, agitation. It will cause tachycardia and hypotension, seizures and coma. Death usually comes in the form of a heart attack, and lung infections.