Well i have n't been slapping for very long but i find it harder to slap on the 3 other strings. The most easiest is the E string where there is little or no chance of contact with the other strings since there is open space. As for the other strings often when i slap with my thumb , it tends contact the other strings producing a unclear tone. Am I doing my slapping worng? I've heard it takes pratice and awhile to get good at slapping the other strings.