When I was little (and yes, I'm so old now!) we had two pigs and one died at 3 but the other lived till 5. We didn't know way back then that you are not supposed to keep just one so we never looked for another friend for her. Now in the UK a shop will not sell a pig alone - only in pairs or a three for sows - and the rescues will want anyone looking for a single pig to bring their other one in to make sure they are a match. Our surviving pig, Snowy, would also call out at night sometimes. We thought she was hoping to be fed but the truth is that it was dark and she was probably calling out for another pig and listening for any response. They do also 'wheek! wheek!' with excitement when they think fresh hay or veggies are coming... even at the sound of a plastic bag rustling as they learn that's what food often comes from!