Cool! Greys are fun to mess with. Not the smartest canine going in my opinion. Actually, I consider them at the bottom in the smarts dept.
I made a stand once and had a grey come out of the woods and sit, staring at my caller. The fox was about 60 yards away from me, and about 45 yards from my caller. I think it was a bird sound that it came to, but not positive. Some distress. Anyway, with no intention of killing the fox, I switched to some coyote vocals just to see it's reaction. Nothing... just sat there. To my surprise, a coyote came in from the extreme opposite end of the field and I shot the coyote at around 100 yards. This would have been 150-160 yards from the fox. I don't know that the fox ever saw the coyote from it's position, but after the shot I scanned back over and that little dude was still sitting there! We can't shoot suppressed here in NY, so I know that sucker heard the 204 bark. It sat there until I got up to retrieve my caller and coyote.