"Molly had that elephantgrey dress with the braided frogs. Mantailored with selfcovered buttons." (U8.163)
From Wikipedia: A frog is an ornamental braiding for fastening the front of a garment that consists of a button and a loop through which it passes. The usual purpose of frogs is to provide a closure for a garment while decorating it at the same time. These frogs are usually used on garments that appear oriental in design. Frogs are usually meant to be a design detail that "stands out".
Many sewers make their own because supplies are inexpensive and the results are customizable. Using larger or smaller size cording or fabric tubes will result in larger and smaller frogs. Also, self-fabric can be used to create frogs that are the same color as the garment, though frogs are usually chosen to be a contrasting color to that of the garment.