Mu!

[...] Kratom's main active ingredient, mitragynine, binds to the same opiate receptor (mu) as opium, heroin and cocaine. [...]
http://www.newscientist.com/channel/health/mg19125711.000

[...]Question,-- whether a Dog hath the nature of the divine Buddha. A reply given by a certain very wise Master is, "Mu!"[...]

M&D, 22