The neighbor gave me a bag of these things... does anyone know what they are?

Củ ấu, also known as water nut, devil's pod, buffalo nut, horned nut, ling nut, bat nut, "mustachioed" nut, or water chestnut. It is a fruit and also a nut that is formed by the water walnut plant – a water weed that can clog dense waterways. The fruits are boiled and the starchy inner part is eaten.