A Han-jee was a green, mantis-like creature with removable eyes, roughly two feet high and four feet long. The optic nerves continue to record and send back images even while the eyes are separated from the body, which makes Han-jee perfect candidates for spying. Hangi have six tentacles that come out the back of their triangular heads. Other beings can put a tentacle up to their own eye and view a playback of the 3D image as if they were actually there. There may be some sort of neural interface involved, as somehow Harvey appeared to both John Crichton and Ka D'Argo while they watched the same "memory image" through a Han-jee's tentacles.
It should be noted that Pilot doubts the existence of Han-jee, believing they are only mythical creatures. He maintains that Crichton foolishly included one of the imaginary beings in his false account of what happened on the pleasure planet LoMo. ("Scratch 'N' Sniff")