What is the test for excusing a juror for good cause?

On habeas review, a trial court's findings regarding good cause and juror fitness are entitled to special deference. Id.; cf. Patton v. Yount, 467 U.S. 1025, 1036-38 & n.12 (1984) (whether juror can render impartial verdict is question of historical fact entitled to special deference). The trial court is in a superior position to observe the juror's physical appearance and demeanor and thereby to determine whether the juror has an opinion or disability that disqualifies the juror or impacts his or her ability to continue deliberating. Perez, 119 F.3d at 1427. Whether a trial court violates a defendant's Sixth Amendment right to a jury trial by excusing a juror for good cause and replacing that juror with an alternate is a question of law. Id. at 1426.