Seamus held his shield against the first onslaught of the birds but they regrouped and came after him again, relentless. They pecked and hammered against his invisible shield - meaning he couldn't do anything else without opening himself up to their fury. "Dirty trick," he muttered, dropping his shield and whirling to blast the window open and force the birds through it with a gust of wind. The arm he threw up in front of his face took a few sharp beaks and Seamus could see blood dripping to the floor almost before he registered the pain.
At that moment, Susan's 'flipendo' caught him off guard and sent him stumbling back into the wall with a muttered 'feck'. Almost before thought he whirled on her and shouted out "Incarcerous!"