Zwieback is a crispy, sweetened bread made with eggs and baked twice. It is sliced before it is baked for the second time, which then results in a crispy, brittle slice that closely resembles melba toast or rusk. Although commonly used for teething children, it also makes a nice breakfast snack which one can use with butter, cream cheese, jelly and peanut butter for example. Medicinally, Zwieback is very good for upset stomachs, as it absorbs acid.