That's part of the automatic decompression release. When the engine is turning very slowly, as when it's being started, a chromed pin sticks out of the shaft near the lobes. The pin holds open one of the exhaust valves for an extended duration. Once the camshaft is spinning up to speed the chrome pin is retracted.
Does anyone know why it's called a "decompression" release? Does it hole the exhaust valve open durinthe compression and combustion strokes?