   .on("mouseover", function(){d3.select(this).style("fill", "aliceblue");})
                .on("mouseout", function(){d3.select(this).style("fill", "white");})
                .on("mousedown", animateFirstStep);

            function animateFirstStep(){
                d3.select(this)
                  .transition()
                    .delay(0)
                    .duration(1000)
                    .attr("r", 10)
                    .each("end", animateSecondStep);
            };

            function a