An example of anthropomorphism in public science discourse:
"There's a natural crevice between the gun and the teeth, and that's where the bacteria can sit, and they think 'Well, he'll never find me here'…
Night time your saliva flow stops, so if you have bacteria on the surfaces of your teeth and in-between, it means while you are sleeping, the bacteria and whatever you have eaten during the day have a little bit of a field day, and that's when they can be most prolific."
Dr Claire McCarthy (King's College London) was speaking on an episode ('Can you be addicted to sugar?') of BBC's Inside Health.
The reference to what bacteria think (which implies they deliberately choose where to be in the mouth based on logical reasoning) is metaphorical, as clearly bacteria neither think nor have any awareness they are in a person's mouth.
Read examples of anthropomorphism in science
'Having a field day' is an idiom (an established phrase with a meaning not obvious from its constituent words).
Read about communicating science through idioms
