Ibululu is a poison which causes Sensitivity, it will give the unknown affliction message but no actual message when it afflicts. As with other sources of sensitivity, this poison will strip deafness if you have it up but otherwise you will see no message when it fires, CONFIG AFFMESSAGES will show you the 'unknown affliction' line.

The poison can be extracted from the following creatures:

Area Creature
Skarch Desert a sand cobra