Cannonball damage actually.

The exhaust pipes are incredibly hot.

Yeah, the pillion passenger has their foot on the foot peg now, but it's previously been on the exhaust -- presumably until they felt the heat as it got a few millimeters from the sole of their foot after melting through the shoe.

If the pillion foot pegs weren't folded out when they started, and they've not been on the back of a motorcycle before, it might not have been obvious where to put their feet.