I was hunting a stand over a field several years ago, on a foggy morning.
A small herd of deer came in front of me, real close, grazing.
I watched them for about an hour, scratching the ground, flicking their tails, etc.
I could hear just a faint "coo" like grunt every now and then from various
members.
Sort of like they were just keeping tabs on each other, while they were eating. Just keeping the herd together.
I've imitated that sound many times since, and swear to have pulled deer in.
Just about as soft as you can make a deer bleat call make a sound.