What makes you remember those who passed away?

Sometimes just a sound or a song or a movie or even a television commercial.

a book， a poem ，a similar one

Recently, Facebook. "Hey! Look at this dead person you knew 6 years ago!"

Maybe something they did impressed me.

Every time I see a dragonfly or a hummingbird it reminds me of my best friend, she loved them.
Like stated before, there are a few times I've gotten birthday reminders for people on Facebook that have passed. I always try to check to make sure they're all still alive before I post happy birthday.