rub a dub dub, sounds of the tub

The other night while bathing Porter lay down to get the shampoo out of his hair and his ears were under water. He discovered that if he taps his bowling fingers (the two middle ones) on his thumb, right on the surface of the water it makes a noise he likes. He sat up and said "mom, next time you are in the bath you have to try this" he showed me and then said "it says Paul Blart Mall Cop, Paul Blart Mall Cop, Paul Blart Mall Cop".