I remember the coins often landed on their heads, or close by. I believe their apparently bored attitude was in hope of some kid (or adult) being lured into thinking the coins could be picked up even from their heads without incident. I always thought, since they never took their eyes off me, I shouldn't trust them for one second.
I didn't know the critters ate them. Sorry (but not much) Oscar was poisoned.
Frankly, the entire pondfull gave me the creeps. I believe the comicstrip, *Pearls Before Swine,* is accurate. Burrr!