Lips will fool a bird. I've seent it with my own two eyes! I am a gargle guy and it does sound more realistic to my ear, but more often then not I find myself not saying a word to a bird that's in range to hear a soft purr. If anything light yelps and bubble clucks are my go to soft talk if needed. My father can't purr for the life of him on a diaphragm but that man is a turkey killing machine and doesn't believe in a shot outside of 30 yards, so even without purring he gets them close and he's stoned more birds then I could ever hope to.