Well, this was interesting. They basically gave an octopus MDMA and then let it decide if it would rather play with a Chewbacca doll or another octopus. The point was to study if octopuses have a system for switching social behavior on or off.
A Conserved Role for Serotonergic Neurotransmission in Mediating Social Behavior in Octopus
A Conserved Role for Serotonergic Neurotransmission in Mediating Social Behavior in Octopus