Within the microscopic machinery of every living cell, a quality control system works ceaselessly to identify and remove defective proteins — yet a new study from Penn State reveals that this ancient cellular guardian is blind to nearly half of a particularly treacherous class of errors. When proteins fold into knot-like entanglements where they should not, or fail to form them where they should, the cell's surveillance often looks past the damage entirely. This quiet failure, accumulating across a lifetime, may be one of the hidden origins of neurodegenerative diseases like Alzheimer's and Hu