Van,
He probably knows that; there's a "bug" in MO when sometimes when you have enough Mudokons for levers/whatever and you tell them to work, some work and some don't know what you are talking about ("Do what?", "There's nothin' to do Abe").
I think it has something to do with groupings of Mudokons on certain parts of levels (i.e., you can't mix Mudokons from different parts of a level and have them work together). It's sort of like certain Scrubs have friends and only work with them. The problem is, they all look and sound a like, so how they tell the difference, I don't know...
The safest thing to do (like Kaimana said) is to have all the Mudokons in a level together when you want them to work; that way, all the appropriate Mudokons that like to work together do.