How are observation and inference different

When you see a tall, young, skinny man walking along the beach, you
observe that a tall, young, skinny man walked along the beach, and from
your observation, you know that a tall, young, skinny man walked along
the beach.

When you see a beach with nobody there, but there is a line of 5-toed
footprints in the sand along the beach, you infer that a human being
walked along the beach.  If you are a skilled anthropologist, with some
talent and experience in a few other fields whose names escape me at
the moment, you might be able to make some careful measurements of
the length, width, depth, and shape of the footprints, and then you might
be able to infer that the person who walked along the beach was a tall,
young, skinny man.  You would build all of your information from inference,
without any observations at all except for the line of footprints and your
measurements of them.

Because shotguns bullets ricochet