Definition: In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.
Input: Article: There are some things humans can go without. We can lose a kidney or a lung, an arm or two and still live perfectly well. But some fish put us to shame. They can _ without stomachs. One such fish is the stout longtom. The group it belongs to carries a more appropriate name: the needlefish. All needlefish lack stomachs. Their ancestors had them, but later they were lost. The stout longtom can reach 1.3 meters in length, and lives near the sea surface. Like all needlefish, it can jump out of the water to escape its enemies. Tropical fishermen are sometimes injured by needlefish. In 1977, a 10-year-old Hawaiian boy was killed when a needlefish jumped through his brain. The longtom eats smaller fish. It teeth are not good at cutting fish into pieces, so it swallows fish whole. Ryan Day from Australia and his colleagues wanted to know how the longtom digests its meaty meals without a stomach, so they ran some chemical tests about the fish. Day's results show that the longtom can consume food without the help of a stomach. It uses a special material called trypsin that can break down proteins without acid -- although the approach is less efficient than using a stomach. Because it's a meat-eating animal, the longtom gets a lot of protein in its food, so it can afford this slightly less efficient system for absorbing it. Two plant-eating fish that Day studies actually had higher levels of trypsin in their body, as their food was low in protein. Day thinks that the longtom and its stomachless relatives might actually have arrived at an energy-saving solution. He says that although the stomach is critical to many kinds of animal, the organ is "a fairly expensive organ to run". This perhaps explains why some animals have got rid of theirs. 
 Answer: digests the smaller fish in its body

Ryan Day ran the chemical tests in order to find out how the longtom   _  .