Final answer:
Rat activity can be indicated by rubmarks, gnawmarks, and empty beer cans.
Step-by-step explanation:
Rat activity can be indicated by rubmarks, gnawmarks, and empty beer cans. Rubmarks are greasy smears left by rats as they brush against walls and objects. Gnawmarks are caused by a rat's constant need to chew on objects to keep their teeth sharp and prevent them from growing too long. Empty beer cans could indicate that rats have been consuming the contents.