Smokey: doesn't care
Reggie: EVERYTHING. fireworks, thunder, balloons, clapping, vacuum cleaner, farts (lol..especially his own), and anything that looks/sounds strange. He did try to attack my mom's new steam cleaner earlier. Both Smokey and Reggie try to kill the paper shredder too.
Nebo: NOTHING. Loves water, attacks everything...really loud noises can possible startle him, but that's about it. He was attacking a water bottle earlier---scared the crap out of Reggie, but it didn't bother him at all!