Some design issues that emerge from few instances of touch-based interactions: different sorts (touch, press, wave ...), different attitude (hold when waiting before your can touch on pic 1), use of different hands (left/right, influence of one's lateralization), the role of signs on the surface to be touched, the surface texture, presence/absence of cues indicating where to touch, multitasking with your hands (holding and touching on picture 3), etc...