From Creatures Wikia
The War Drum is an instrument found in the temple of KT. When hit, it will make any Creatures that are near it extremely angry and will cause them to hit or even kill each other, making it a very dangerous toy indeed.
A second, makeshift solution is to open up the CAOS Command Line by pressing Ctrl+Shift-C and type in
enum 4 0 0 urge writ targ -1 2 -1 2 next
to cure all Creatures. Typing
urge writ norn -1 2 -1 2
will cure the selected Creature.