This is the final inspection station. The red flash on the front of the engine is from the scanner in the inspector's hand, which he's using to read bar-code stickers on different critical components on this Three-Valve. You can see a monitor in the background on which there are currently some green and yellow rows across the screen. Individual rows remain yellow until the respective sticker is scanned, turn green if the anticipated sticker is in place (meaning the correct component), or red if it isn't. A red code will stop the assembly line.