Shudder in its tracks

This was found in the Ars Technica website, a site covering news and opinions in technology, science, and politics.  Here is the full quote:

“That ruthlessly efficient system helped bubonic plague kill nearly 25 million people and made the ancient world shudder in its tracks during the Justinian plague of 541–542.”  https://arstechnica.com/science/2018/06/4000-year-old-genomes-point-to-origins-of-bubonic-plague/

It is a conflation of “shudder to think” (afraid to think about something as it may be unpleasant) and “stop/freeze/halt (someone or something)(dead) in its tracks” (suddenly stop because something has frightened or surprised you).  Considering the context, the author might have been thinking about death and the word “dead” may have been floating around in the head, spewing out “in its tracks”.  A big thanks to Barry Eigen for spotting this one.  Barry said the malaphor also reminded him of the expression “shaking (shivering) in their boots”.  Me too!