The bacteria are found by looking at the scratches on the teeth

Yes, you heard right.He actually discovered bacteria by looking at dental scrapings,which, when you keep in mind that people didn't brush their teeth much -- if at all -- back then,he must have had a lovely bunch of bacteria to look at.When he wrote about his discovery,he didn't call them bacteria,as we know them today.But he called them "animalcules,"because they lookedlike little animals to him.While Leeuwenhoek was staring at his teeth gunk,he was also sending letters to a scientific colleague in England,by the name of Robert Hooke.