So one thing I found odd in the DM's Basic Rules v0.1pdf was a large list of animals that seemed so insignificant as to wonder why it was included in the PDF. For example, the "Rat" monster, has 1 hitpoint, and a CR of 0, it can hit for only 1 point of damage with a +0 to hit.
However, I then noticed that there are swarm creatures, such as a "Swarm of Rats" which has 24 hit points, +2 to hit, 7 damage or 3 damage when it has less than half it's hitpoints, and is listed as "Medium swarm of Tiny beasts". Swarms also have the following trait:
The swarm can’t regain hit points or gain temporary hit points.
This made me think that this was very neat. A swarm is made up of indidvual creatures, and each hitpoint means each creature died. So for a swarm of rats, I might think this means that there are 24 rats in the swarm.
But is this actually the case? When a swarm is reduced to 1 or 2 hitpoints, should I switch those out for actual rat creatures? (This would basically cause the swarm to lose the damage resistances, immunities and reduce the amount of damage it can do.)