The expression of total concentration is one of the most reliable pictures at any gathering. Heads dipped under a raised bonnet, two people bent over the same detail, the frown of someone studying, judging, examining, appraising.

Where it works: a car show (studying an engine), an antiques fair (inspecting a find), a dog show (a judge's assessment), any competition or collectors' event.

Best time: wherever people are inspecting rather than chatting.