This is true. My mother gave the story many years ago at work when someone was trying to open a jar of snails (yuck.) Apparently, the jar was passed around everyone present, and NO ONE was able to open the jar.

When it came to my mum (and this is the secret), she tapped the edge of jar around a few times on a hard surface, and then she was able open it. Everyone was astounded she was successful.

As 'a prize' she was offered a snail from the jar, but (wisely) declined.