Yes, it's the kiss that either works or doesn't. Sometimes I'll just keep on having the couples "kissing" over and over again until I see the count goes up.

Once I was trying to recover my population quickly after a bunch of geriatric babyboomers died, so I picked a male and had him go around "kissing" each of the females until they each started nursing. I don't think he went into the shack at all, the cad.