I've had cats for over 20 years. My newest cat is a 2 year old neutered Ragamuffin and is an indoor cat who has access to a catio. He is lovely, affectionate and loves human company. Recently he has started humping a particular cushion which is soft and has long threads. This is starting to happen every day now. I've never seen this happen before with my other cats. Should I worry? Is this normal?