rotorspin
Think high and low pressure areas - that's alleged to be why the door stays open a modest amount until down to @60kts IAS or less. By modest amount an SK76 door will be open @3-4" at 140 knots. It's not so much the amount the door is open that generates a thread but the explosive nature of it doing its thing that garners the attention; that and the fact that the only way on that aircraft to get it closed is to slow down, a lot. Not great fun when IMC, but doable.
I never really had a problem with this until flying the BH222 and SK76 - suspect it was self induced by not paying proper attention to closing/locking doors!
Seems perfrej got the right training on this problem!
WIII