Vistors to an interactive science centre were observed while assembling a large‐scale lock and key kit. Males, and those who had previously watched another visitor, were faster at initial assembly of the lock, but for males this speed advantage disappeared in a reassembly test. After spending time with the exhibit, 70% of the visitors could provide a full description of the workings of the lock, but neither their provision of a description, self‐assessment of understanding, nor reported past experiences, were related to reassembly time. What counts as ‘understanding’ an exhibit is discussed.