In Russian, молния means both lightning 
and zipper!
So when you hear сломалась молния, don’t picture a thunderstorm, it might just mean someone’s jacket zipper broke.
And what about собачка? 
That’s the little slider, the part you pull to open or close the zipper. Funny, right? Russians call it собачка (literally “little dog”) because it “runs” up and down the zipper like a small dog on a leash.
Example:
— У меня сломалась собачка на молнии.
— The zipper pull on my jacket broke.
