Ducks will occasionally cough on their feed, especially when the feed is on the powdery side. In most case's all that is needed is water provided, and eventually, they'll get it down. I would not use your finger to clear a blockage. Several times, I've had teen-ducks try to eat chad, and end up getting it stuck in their throat. Even after a few minutes, the fish was still lodged in there so I had to lube up a catheter and push the fish down. Doing that would be something I would only recommend for serious cases, as pushing whatever the object is down their throat could possibly end up scratching or severely damaging the inner esophagus lining.