Five experiments demonstrated that 6.5-month-olds perseverated in a violation-of-expectation task to examine reasoning about width information in containment events. After watching a familiarization event in which a ball was lowered into a wide container, infants failed to detect the violation when the same ball was lowered into a container half as wide as the ball. A problem-solving account of perseverative errors in means-end tasks was used to interpret results. (Author/KB)