I'll drop in a random objects in, like the old (clean) lid from a fish foot container, etc. Shamum is hilarious. He flares his fins just a bit, gets all sideways like a cat and floats backwards away from the object. After about 5 or 10 seconds he's totally checking it out. If it's something big enough for him to swim into he will.
I noticed last night, in an attempt to get him to pellets ( I drop him one or two daily just to keep trying), I dropped in about 5 pellets on accident, so in an attempt to retreive the extras before they sank I stuck my finger in to pull them to the edge of the tank. Shamus attacked the one pellet I was going for as if I were another fish trying to take his meal.