communication

Is there a reference post or helpful website page listing the meanings of the various noises? I've recently switched a few things around and there's being more aural communication than before, so I want to be sure I'm interpreting things right. I've seen that there's a couple mentioned in the...

i just witnessed my younger pig - charlie - nibbling/nudging my older pigs ear. she wasn’t complaining though, she just closed her eyes and allowed it. is this normal between pigs and what does mean?