Whack all but 2 blackberries and 2 Raspberries into a shaker, and give a very quick, hard shake, really get the froth going on the pineapple juice. Double strain into a chilled martini glass, having a muddler to hand to push the final parts of the white foam onto the drink, garnish with an arrangment of berrie on the glass, and two straws to the side. mmmm, perfection of a classic