The bamboo disk.
Back in Metru Nui, Kanoka Disks were the primary tool of most Matoran and came equipped with all sorts of powers - reconstitute at random, for example, can scramble the molecular structure of an opponent, completely reforming them into a different shape with the potential to kill them.
However, the Kanoka disks and the mechanisms required to launch them were left behind in Metru Nui when the Toa Metru mirated the inhabitants of the island to Mata Nui. They then developed the bamboo disk, identical in shape and size to the Kanoka, although powerless and light enough to be lobbed by the average Matoran with enough force to combat a Muaka, the apex predator on the island.
In fact, Matoro, who considered himself the furthest thing from a hero, was noteworthy as a Muaka hunter, using the same bamboo disks to take down his prey. It’s only when the same Rahi were captured and corrupted by the Makuta’s infected Kanohi that they became too problematic to handle.
Incorrect; it was just really good timing.
A Muaka is a wild, territorial Rahi. The Matoran acted accordingly.
There is no Bionicle equivalent of rabies, however the Makuta’s corruption via the infected masks made otherwise docile Rahi violent and vicious, and normally antagonistic Rahi became serious threats. In fact, in numerous situations, the Rahi proved too much for the rookie Toa Mata to handle.