Original Question: What makes bay leaves poisonous?

They’re not poisonous, it’s an urban myth - Bay Leaf, is it toxic or what?

The myth probably arose because some shrub species which are commonly called laurels, such as the cherry laurel (Prunus laurocerasus), but which are actually unrelated to the bay (Laurus nobilis), can be toxic since they contain small amounts of cyanide and benzaldehyde.