Bathtub Drain, Two Ways

Susan asked her son to remove some hair that had collected in the grate covering the drain in the bathtub then watched in horror as he took the hair, threw it into the toilet and flushed it away.
At the very end of Susan's shower she noticed she was standing in a half inch of water. She took her foot and played with the lever. Nothing happened. 
She got out and plunged until she was sweaty and wracked with old age pains. Nothing happened.
She asked her son to plunge. Nothing.
She went out with her little sister and returned with Drano & a snake which her son took and went to investigate. A few minutes later he emerged and asked if Susan had been messing with the lever. 
She may never learn why the tub was a little slow to drain but apparently she sealed the drain opening shut when she flipped the lever the wrong way.