Why are they called practical jokes??

Sometime in the last few months Violet and I started playing jokes on each other. She vasolined the tolet seat and I short-sheeted her bed. She stirred horseradish into my cole slaw so I TPed her room. She added more stuff to my supper and I put candy in her shoes. I just went into my bedroom and she has struck again; I will be picking up TP for awhile. So, tomorrow while she is gone I'm going to stretch cellophane across the opening of her bedroom door. We have fun and laugh alot but I am running out of ideas. Anyone know some practical jokes?