What is Schmagnum?
1.
The thin, gummy film that forms on geletin (Jello) after sitting in the refrigerator for several days.
They knew the geletin was old because of the schmagnum.
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2.
A tough, thin film that forms on the surface of geletin (Jello) when left sitting in the refrigerator for too long.
He could tell the geleting was old because of the schmagnum.
See