In the early phases of the Fall, before anything was known of the TITANs, the world simply seemed to be becoming strange and worse. The planet was already in a state of ecological turmoil, with animals being pushed out of their normal habitations and into contact with humanity. Some actions seemed definitely beyond what could be explained by desperate hunger, increased competition, or diseases such as rabies. Rats occasionally swarmed from drains, attacking even large groups of people, family dogs might suddenly run off in terror, biting at their former friends and never trusting them again, and many people lost their eyes to birds.
The culprits were animal-oriented basilisk hacks, inducing in their victims a frenzy of rage and terror. With simpler effects and operating usually on less complicated brains than those of humans, the hacks were commonly made by basilisk weeds. Apparently there was a hack for each species, and even today it is best not to take animals into TITAN zones.
Inspired by Arthur Machen's The Terror.