Please help me with a phrase (it's given in "[" and "]")
"The Gray Man knelt and pressed the barrel of the gun to Declan’s stomach, which rose and fell calamitously as he gasped for air. [Tracing the gun over the boy’s right kidney], he said conversationally..."
What did the Gray Man do with the gun and boy's kidney? What does "trace" mean in this context?
Thank you very much in advance!