How big a LMB does it take to eat a big bullfrog?
Big enough for the frog to fit in it's mouth.....
I DID watch a LMB in my pond grab what seemed a YP that was 10+-11" long, flare it's gills and mouth, shake it's head and spit it back out.
I'm guessing that either the YP dorsal spines or gill flap spines made it a wee bit uncomfortable.