The dried fruits can also become darker and considerably harder than they look when fresh.
This explains why the objects in the photograph look almost like pieces of carved wood rather than something edible.
Are They Actually Edible?
Certain species of water caltrop are traditionally eaten.
The inner seed is the part that is generally consumed.
The tough outer shell is removed before eating, much like the shell of a conventional nut.
However, this does not mean that every dark, horned object found in a bag should automatically be eaten.
Correct identification matters.
The safest approach is to confirm the plant species and make sure the fruits came from a legitimate food source before preparing them.
If your neighbor simply collected them from an unknown body of water, eating them without knowing exactly what they are would not be a good idea.
How Are They Traditionally Prepared?
When water caltrops are being sold as food, they are commonly cooked before the edible seed is removed.
Depending on the variety and culinary tradition, the fruits may be boiled or otherwise cooked until the interior becomes easier to access.
After cooking, the hard outer shell is cracked or cut open, and the edible portion inside can be removed.
The texture of the cooked seed is often described as starchy and firm, somewhat comparable to other starchy seeds or nuts.
In some regions, they may be eaten as a snack or incorporated into other dishes.
The shell itself is not the part you eat.