The level of medical advancement we’ve seen over the past 500-plus years has been astronomical. Just look at how Europeans handled the Black Death, aka the plague, when it came off Genoese trading ships in 1374, and spread indiscriminately throughout the continent. It would go on to kill over 20 million people — almost a third of the population — but before death, those infected would experience painful black swellings of various sizes under the armpits and in the groin. These eventually began to seep blood and pus, after which the patient would have a fever, diarrhea, aches and pains; and eventually, they’d die.

Scientists had no idea at the time that the disease was caused by the bacteria Yersina pestis, and therefore, how to stop it was out of the question. One doctor, for example, believed “instantaneous death occurs when the aerial spirit escaping from the eyes of the sick man strikes the healthy person standing near and looking at the sick.” When it came to medical technology, many were trying unproven and crude techniques like bloodletting or boil-lancing — literally stabbing the boil, which can even cause the infection to spread.

Luckily, science is always evolving, and these techniques were improved upon substantially over the next few hundred years. However, to get to where we are today we had to make mistakes, and experiment, just a little bit. The products of some of those experiments were actually quite terrifying. Here are five of them.