I can't find the link now, but I saw one where a guy had taken a bunch of these cheap bats:
Animated Flying Bat Decoration in Decorations Rodents, Reptiles & Insects
and glued them on to a piece of wood, hanging upside down from the ceiling, he had hacked the motors so he could turn the wing flapping on and off remotely. It was apretty cool effect to have all the red eyes looking down at you from the top of th bat cave and then have all the wings start flapping.
While the bats are not that great to look at in the daylight in a dark cave like room, they can be pretty spooky.