RE: I don't understand
It may be because the question has been addressed a lot in the last couple of weeks. Try doing a search for bleat calls, or calls in general, and you'll find a lot of stuff on them.
On a side note, I have been coming here religiously for the last month or so and I have noticed that questions on calls and scents, in general, are not looked at or responded to as much as other topics. Again, that may be because the old timers (to the board) have seen the same questions year after, month after month, and day after day that they are no longer interested in reading them or replying to them. It could also be that many don't use them so they have no opinion to give.
When you do your search, make sure to hit the right forum (Bowhunting and Deerhunting would be your best shots, but they have to be done separately) and pick the 30 day search period. You'll get a good set of hits and your question will likely be answered.
-Brad
Eastern Nebraska Bowhunter