It's not the crappie seeing the minnows in the jar that attracts the fish. A crappies sense of smell is 100x that of a blood hound. The fish not only smell the minnows through the holes in the lid, the minnows run into the sides of the jar causing a ticking sound that is the dinner bell for a hungry crappie. I actually did this one time and noticed the line with the gallon jar going crazy. I pulled it up and a bass had swallowed the gallon glass jug halfway down. Of course, with the jar being slick, he came right off. I would have had a shot at landing him if I woulda let him swallow the jug a couple inches deeper.