phrases

anybody know the origin of the phrase someone walked across my grave or someone stepped on my grave? my grandmother, who was german but grew up in the states, used to say this. was it said in the uk?

I was wondering about the origins of some odd sayings, such as... Let the cat out of the bag. The balloons gone up. raining cats and dogs. Flying in the wind. Carry the can, and my favourite..For Petes sake, any ideas?