The Sa Giang (company name) Vietnamese prawn crackers are sold as a package of small, dried, and round chips. They are deep-fried and expanded to the bigger, crispy, and oily chips that are typically served with Vietnamese salads. They are to be eaten together with the salad as a scooper, but you can eat them by itself as well!
Below is a GIF (made in Google+) that shows how quickly the chips are expanded when deep-fried.
Wikipedia has some more info about the Vietnamese prawn cracker:
Sa Dec in southern Vietnam is the home of bánh phồng tôm. The traditional snack is made of ground shrimp, sometimes mixed with cuttlefish, arrowroot flour, tapioca flour, onion, garlic, sugar, fish sauce, cracked black pepper and salt. Traditionally the dough is steamed, rolled out, cut into round chips then dried. Another method is to form rolls, steam and then slice into thin rounds before being dried. Modern production favors the oval shapes such that the chips form a “scooper” as an accompaniment to salads (gỏi and nộm). The brand Sa Giang is well known.