Do you zummish?

My grandfather(1896-1980) frequently used the expression "Do you zummish(zoo-mish)? Or just said Zummish?, meaning "do you understand"? I've not been able to find this word anywhere. They lived in north central Pennsylvania with a strong German heritage in the area. Please help if you can. Thanks

That is a interesting phrase. Unfortunately, my Historical Dictionary of American Slang ended at O (because of a dispute) and the Dictionary of American Regional English is only up to S. I've been looking in other references, but no luck so far.