Case 1: Verb is out-of-band.
- Because S sells office products, and M is a purchase order, we
assume that S is supposed to ship products to C and debit C's credit
card.
- Whereas, because S2 is a message logging service, we assume that
S2 is supposed to simply log message M.
- I.e., meaning of the interaction is established out-of-band,
either by convention or negotiation.
