Understand snag in operation (5,2)
I believe the answer is:
Here is my best explanation:
'understand' is the definition.
'snag in operation' is the subsidiary indication.
'snag' becomes 'catch' (I've seen this before).
'in operation' becomes 'on'.
(Other definitions for catch on that I've seen before include "twig", "Get it", "Understand - become fashionable", "Become popular" and "Informally, become popular or come to understand".)