Actually slapmarking is quite easy, and pigs seem to suffer from transient pain - that is they jump and then seem to go back to normal.
You MUST slapmark on both shoulders - Pigs Records, Identification and Movement Order 2007, part 3 section 6 (2):
"..., or by slap-marking equipment, in which case it must be on each shoulder."
We slapmark as they are eating, it is a good slap done with purpose, but is just tatooing the skin. The pig will typically jump and squeel, but within a few seconds go back to eating - you then slap the other shoulder. After slapping they seem to suffer no effects, and many times I have slapped and then sat with them for a belly rub (theirs!) so they do not go off you !!
If you are getting them back as halves there is no point in doing the rumps also, as that would then be to suspect your butcher as well
