Spike’s tongue is deep inside Sweetie Belle bowels, her belly shows outline of the tongue.  
Sweetie Belle is swallowing and pushing cum inside her belly, forcing it to squeeze around Spike’s tongue into his mouth. When Spike moves tongue deeper, her throat and lip muscles can’t hold the cum and she is vomiting it onto Rarity’s tail.  
Rairty throat is stretched and sealed by the dragon’s dick knot, so his cum is now escaped through the other exit.  
Both ladies have orgasm from intense streching, Sweetie Belle orgasm fluids goes into Spikes mouth mixed with cum from her ponut.

imported from https://derpibooru.org/images/2089448