Whilst playing the latest experimental build, I had the misfortune of coming across a Fungaloid. It attacked me, I defended myself, and upon delivering the killing blow to the ambulatory fungus, the game shut down. It didn’t freeze, no error message in the log or anything like it. It just quit.
Either this is a bug, or the Fungaloid is a much more formidable foe than I had anticipated, capable of killing the very reality it resides in.
This problem can be reproduced by killing a full-grown Fungaloid. Confirmed to be present on a fresh installation.