JT- Funny you should ask. Sometime soon, there will be a 2-part series in Trapper magazine covering this very issue. I strung the words together with the help of a couple master callers, notably Rich Higgins in Arizona. Don't miss it because part 1 outlines the four main howls and how to make them, and part 2 builds a foundation upon which you can develop your own howling technique. Long story less long... I'm not familiar with an interrogation howl and don't know how you would distinguish it from any other lone howl, but knowing how to do a lone howl is a good way to start. I start my stand with a lone howl. Wait a couple minutes. If I get a verbal response, answer back. If it's a threat bark - 2-3 short barks followed by an almost screaming wavering howl that the coyote repeats - threaten him back in the same manner. Oftentimes, he'll come in if you're near the territorial core. If he's just barking at you, do a high pitched ki-yi to simulate a pup in distress. Under no circumstances should you just bark (unless he barks first), since there is no such thing as a friendly bark to coyotes. If no response, go ahead and use rabbit squeals, adding in a lone howl once in a while. Remember, lone howls have umteen meanings to coyotes. Others will tell you to use them as locators. Don't do it. You'll ocasionally get one to answer, but in far more cases they'll just come in to investigate you. Howling is much more complex than regular calling, but the study time is well worth the effort. Good luck. (BTW, we're hoping for the pieces to be in the Dec. and Jan. issues, but no guarantees.)