For anyone who has pets, dumping out any kind of pin out before using is not a good idea and storing safety pins open isn't either. We have to be extra careful when we have furry family members we love.
Even as careful as I try to be, I have caught our little Penny running around with a straight pin in her mouth on more than one occasion. I say to her "What have you got?" And the jubilation leaves her expression, is replaced by an "Aw...Crap!" kind of look, then she drops it on the floor for me to see. I was pretty horrified the three times it was a straight pin.
Humans have to watch out too. My mom was a sew-er. I always hesitate to write "sewer" ;). She used to regularly lose straight pins in the shag carpeting. My Dad's foot always found them. Ouch!