Reading up on the features of my recently-acquired 2012 Mazda2: it has a timing chain, not a belt & is a non-interference engine. This means if the timing chain should somehow fail, the pistons do not move far enough into the cylinder head to come into contact with any open valves.
Having experienced a bent valve stem with a car with an interference engine, this is a good thing. The piston in that case drove the edge of the valve into the aluminium alloy cylinder head, leading to a $600 repair bill. This was in 1982, $600 went a heck of a long way in those days.