you can't just read a molecule and say "oh it looks like something safe". Digitalin and the cardiac glycosides [1a,1b] may look like completely innocuous compounds (just have to remove a group and they are inactive). Some hormones look like cholesterol. Some steroisomers [2] (think of it as just changing the order atoms are connected in space but not what they are connected to) of molecules kill you while some other forms are safe and that's even harder to grasp on a 2d representation of the structure.