On Saturday I went out in a Pacer (small sailing boat, designed for two but can take four people if some are small), and before I'd realised how small they are the boom came across unexpectedly and thwacked me in the cheek. Since I hadn't seen it coming this took me rather by surprise.

The photo on the left kind of shows the consequences a couple of days later (I freely
confess that you can hardly see anything, but the consequences are slightly more visible
in real life); the photo on the right shows what the consequences should have been if they had been commensurate with my perception of the impact!