[Dan Borufka]

I would create several small splash sprites to emit using Trapcode Particular or one of the particle emitters already built into After Effects.

[Dan Borufka]

Pingo, why not add another expression control on your book comp to select and animate the index of the layer/page that should be used?

That way, you could animate a slider (let’s call this one “pageIndex”) and integrate that to your expression.

var pageIndex = Math.round(comp("book").effect("pageIndex")("Slider").value);
comp("book").layer(pageIndex).effect("Slider Control")("Slider")*0.01;