Hi, we have had our two girl piggies for a few weeks now and they seem to be getting a bit more settled now. They don't seem to like being caught but once I have hold of them they are happy to sit on our knees and nibble their veg. Today while my little girl had poppy on her knee she kind of started almost vibrating?!? Kind of felt like a cat purring but with no noise. Is this normal and is it a happy or a sad thing? Also will they eventually get easier to catch?