Subject: What is the mechanism for the decay of the charged pion?

The lifetime of the charged pion seems to clearly indicate that it decays 
weakly. The products are a muon/antimuon and a muon neutrino/antineutrino. The 
products can clearly be generated by decay of the W+/W- particle, so I 
initially thought that the charged pion "turns into" the weak vector boson 
which then decays. However, the pion is spinless and the W particles have a 
spin of 1!

(I did send a question about how the rho meson can decay to a pair of pions, 
and the response was that the pair of pions is a two-body system and thus they 
can carry away angular momentum. Is it still possible for a single body?)

Re: What is the mechanism for the decay of the charged pion?