I dunno what it is, but sometimes some herps just "don't get it" about particular types of foods. It's most common in snakes, of course, and there are all kinds of tricks that have been devised by clever (and desperate) keepers. Some snake species are ridiculously picky, and nothing but the right kind of centipede or blindsnake will do; others seem to transfer acceptance fairly easily once the association is made a time or two, and then there are things like cottonmouths, which will happily eat link sausages, or canned cat food from a bowl (kids, don't try this at home).
Monitors are pretty much on the cottonmouth side of the spectrum, but you'll find some quirks. My old female croc (WC) was terrified of any roadkilled snake I offered, wouldn't eat rats or squirrels until either she or I had removed the intestines, and liked birds best; she was always manageable at feeding time until one day I offered her a pigeon squab, and all hell broke loose. That one sure liked squabs.
Feeding preferences (or a willingness to try almost anything) are probably pretty well set by the time you start caring for a WC monitor, but with CB animals their exposure to various prey types has been really limited, and you may need to show them a time or two. My current (CB) crocs had no idea what pinkies were -- they walked over them, and simply pushed dead whole mice around, even though I'd been feeding cut-up mice. I just skinned the whole mice a couple of times, and that was all it took. With your reluctant animal, try smearing some waxworm goop on the mouse, or mix some waxworms on a plate with a cut-up mouse, and I bet you'll soon be past that hurdle.
Hard to believe, but you can count up the scientific papers on the natural history of V. gouldii without taking off your shoes, and Daniel's book lists them all (under V. flavirufus). Graham Thompson's papers have the most detailed information.
