Volitionality and passing gas

In Sherpa, like in other Tibetic languages, a distinction is made between volitional and non-volitional verbs, meaning that when you describe an action in Sherpa you usually need to specify if it is either 'on purpose', or accidental. In English this distinction is sometimes made lexically with verbs of perception, as in the difference between 'seeing' and 'looking' (or 'watching') as well as 'hearing' and 'listening'. However, in Tibetic languages, this distinction extends to most other verbs as well.

While there are some interesting pairs, my favourite one so far from the Sherpa-English dictionary is:

སླེན་ཤོར་ pen shor (v.inv) = to fart (involuntarily)

སྤེན་གཏོང་ pen tong (v.vol) = to fart

How volitionally can one fart?