Sand Sifting Crabs (from here). Put them in, they burried down, everything was great...I was thinking to myself "ok, this is going to be the cleanest sand bed in history!"
Left the next morning for a trip, came back, and it was like a crab leg salad had been dropped in my tank. I guess my Snowflake Eel liked hunting them under the sand...they lasted about 24 hours...out of five, all were gone when I came back.
On the flip side, at least the eel was not hungry when I was gone.
You live and learn.
Stewart