Perk idea: soft touch.
Soft touch lets you pet more or less any denizen, making hostile denizens docile... at least most of them to pet, you do what you do to pet the strider, I.e. grab repeatedly.
Special interactions: normal Barnacles can't tell the difference between most things, so though they make a sound, they don't stop trying to eat you if you touch their tongue. Teeth will hesitate, but his hunger won't let him stop. Mechanical denizens have no nerves, so they don't feel you petting them. Moth whelps try less to shake you off. Spriders are pack animals, so one is content with you, it tells the others. The mass isn't pettable, and neither are its offshoots, sorry. Aunts care more about what mother says about you, so petting them doesn't do anything other than make them make a sound if they're docile. I imagine mother and the vendor has special dialogue if you pet them.