Exploding rats have been around for a long, long time to clear the sewers, strongholds, and to add colour to a boring ceremony.
The advent of sorcery has made the practice less labour intensive than in those years of old.
However, the lost art of exploding rats (and the occassional unfortunate) has seen a return to tradition for those who distrust the magical arts, or who prefer to reduce the costs of outsourcing their explosive needs.
As the old sage says,
You must be careful in the room,
Filled with rats that can go boom,
Count your fingers before and after,
Lest you end up with a finger disaster.
So keep your digits safe and sound,
And don't let them go flying around.