The place where blood clots are most likely to form These are places of narrowing, branching and steep bends of the vessel. The animation shows an example of a bifurcation - splitting a vessel into two branches. Why is the risk of thrombosis higher here? It's because of the turbulent blood flow. Normally blood moves almost like a pathway - with minimal bends and no "obstacles". But here there's a bend and an obstruction in the form of a partition between the branches. Blood ends up "clinging" to the vessel walls, which causes it to accumulate in the place of whirling.