One way to infer the possibility of non-human existence is to observe those medium who could summon spirits and communicate with the dead. Some are eerily accurate in assessing the issue at hand faced by the client. Ghosts and spirits have abhinna powers too! The medium might not be summoning the actual dead family member or relative, but some lowly spirits or peta who are severely deprived of merits. They are in such a pitiful state of deprivation that they are willing to possess a filthy human body to make the medium enter a trance and convey message to the client, thinking that they could make merits this way. The higher devas would never want to even come close to our filthy bodies. We smell too badly for them.
Paranormal accounts related from family members, relatives, and friends help too. Since young I am intrigued by stories of the supernatural world. My late maternal grandmother and my mother saw deities before. I don’t think I have any reason to doubt them. I personally have encountered some strange happenings/sightings which really led me to strongly believe that non-human is not a figment of our imagination.