animals can't detect poison ?

No he could not. He was a silly monkey.

Nazi monkeys lack this skill, evidently. This genetic mutation is why there are so few left today.

Many poisons are undetectable by man or beast. How many animals die from carelessly discarded antifreeze every year, or even from eating human foods that are dangerous to them?

You never heard of rat poison? I find that strange from someone named Rateater.

My guess is the monkey was starved and hungry, and took a huge bite out of the date before it noticed the bitter taste of the poison and realised it was too late.

If they used a poison a monkey could detect, it stands to reason that a human being would be able to detect it as well. The assassin clearly chose a tasteless poison, which would obviously be tasteless to a monkey as well.

It was iocaine powder.