There are 499 customers on mail carrier Tracy Herron's San Leandro postal route. She knows most of their names.
After delivering the mail day after day, year after year she got to notice things.
For example, some customers didn't like getting mail, and would let it pile up for days.
Others couldn't wait to dive into their pile of letters, bills and junk mail.
So when the mail began to pile up at the house of an elderly woman on her route this week, Herron immediately got a bad feeling.
"That was weird to me because she picks up her mail every single day," said Herron, who's worked for the U.S. Postal Service for 15 years.
Herron decided to wait a couple days, in case the woman was merely ill.
On Thursday, with the mail continuing to pile up, Herron began knocking on neighbors' doors to see if anyone knew the woman.
"I'm like, I think we need to get in there and see what's going on because something's wrong with this lady," said Herron. "I believe she's in there and she's not ok."
Although Herron had never spoken to the woman before, her hunch was right on. Police entered the house on Cleveland Street through an open back door.
They found the woman on the floor, suffering from a stroke.
A pot on the stove had melted. The woman was hospitalized and Herron said she was in intensive care.
After her astute act, Herron did what she normally does - she went back to delivering the mail.
"Just as a person," she said, "It's good to look out for other people."