I don’t know why, but many hunters are either reluctant to use a bull grunt or, on the other hand, use it too much. If you moan and a bull grunts back, take the time to estimate how far away he is. Also consider whether he’s grunting frequently or sporadically and, most importantly, whether he’s closing in. Each situation is different, but if you hear a bull coming, sit tight and let him. He knows what he wants and he’s coming to get it. If a bull is grunting with a regular cadence, chances are he’s coming in on a string. Thinking you’re his breeding prospect, he’s grunting to let you know he’s on his way. Grunt back at this point and it could go either way–he could continue and challenge the competing bull or he could back off altogether.
While bulls are curious, they’re also notorious for sometimes playing hard to get and hanging up. When a bull hangs up outside of shooting range or under cover, he’s cautious, but he’s also motivated to breed and knows there’s a cow nearby. This is when a couple of guttural grunts can push him over the edge and bring him in. If you grunt shortly after moaning, the bull should interpret those vocalizations to mean a competing suitor is already tending a hot cow. This is sometimes enough to bring him in to challenge the bull and, in turn, present you with a shot opportunity. But realism is paramount. Grunt too aggressively and you could dissuade the bull from coming any closer. In the end, it’s about interpreting the bull’s mood and calling accordingly.