Hmm. I'll have to see if I can track down a video. What I was watching today on RFD TV was called "Horse & Country" and it was a British (I think) guy doing a dressage demonstration.
I also heard it on a video that was posted here at the horse forum a while back. I *think* it was perhaps Anky(sp?) when she was demonstrating long and low, or long and deep, or rolkur? I dunno, I get all the dressage stuff in a jumble! But the dressage people seem to do it the most.
If I find a video I will post it. But if anyone else knows of a video offhand and wants to post it, that would be great too!
I know just what you're talking about! A few people at my barn (including my trainer) make this noise and I also saw that same show you're referring to. It definitely seems to be exclusively in the dressage world from my observation.
At my barn I hear it mostly used to slow down a gait, not stop, though. They still use "woah" or "hoe" to stop.
I prefer to use eeeeeeasy to slow my guy down and hoooooe to stop. But I was raised in a western saddle, so I may not be the best example ;)
I use it to get my horses to slow down on the lunge and occasionally undersaddle. To stop I use "whoa".
It doesn't have a name in English really... It's the same as saying "easy". My horses understand it to mean to slow down in a gait, like clucking means to go faster in a gait.
Totally a European thing, a lot of North Americans don't get it. I picked it up off Kyra Kyrkland, and when I had a mare from Europe she didn't know English voice cues so I had to use the purr noise.
I actually had a manager at a barn I was working some young horses at ream me out for using it...