[VLM]

He's talking about cassia, and the specific substance is coumarin which has a fairly high fatal dosage for humans. Note that cinnamaldehyde tastes really good and has nothing to do with coumarin if the chemical processing is done correctly.

Anyway in rodents at very low doses their liver converts it to some nasty epoxide which slowly gives rodents liver cancer; not an issue for primates who an only die from acute liver toxicity.

This was a "thing" generations ago, leading to endless old wives tale type advice about cinnamon "repelling and killing mice" which actually doesn't work because its too bitter if dusted around in pure form.

If you're bored its interesting to research cinnamon-flavored liquors, the more "natural and organic", at least if it uses cassia for flavor, the higher the poisonous coumarin content and in contrast the more processed refined pure cinnamaldehyde is essentially non-poisonous (lethal dose for a human would be about half a liter of the concentrated oil, extrapolating from animal studies, figure a percent or two of total body mass). From memory the LD50 of common table salt is about 10% lower than the LD50 of cinnamaldehyde, of course in a cinnamon flavored liquor the ethanol would kill a consumer long before the cinnamaldehyde would be an issue.