Here’s one thematically similar to Sunday’s kotowaza:

窮鼠噛猫
kyuu.so.gou.byou

Literally: destitute / suffering / cornered – mouse / rat – bite – cat

Alternately: A cornered rat will bite at a cat. Those in desperate straits will become unexpectedly fierce. Nobody fights like someone who has nowhere else to turn.

Note: This four-character compound can also be expanded to 窮鼠猫を噛む (kyuuso neko wo kamu), which as you can see is just the same thing with some grammar thrown in.

Pyao pyao pyao!