A Common Loon was thrashing around as if trying to beat a shellfish that it had caught into submission. But what it was actually doing was positioning its catch to be swallowed. Loons typically eat fish but will grab shellfish and crustaceans as well. They, and ducks that eat shellfish, can’t crack the shell so they just swallow it whole and let their powerful gizzard crush it. But they apparently like to have their catch oriented for a smooth trip and toss the prey around until it is where they like it. These pictures capture some of the activity, including the big lump in the throat as the meal goes down.
After all the work, the Loon settles down while the gizzard does the rest.