Slap marking is easy peasy too, and again, 99% of the time they don't bat an eyelid, especially if you do it while they are feeding. The only downside is having to buy a slapper with your herd number on, which is quite expensive, but if you are going to keep pigs for several years, it is well worth investing in one. It is not unkind or cruel at all and I don't believe it causes anything other than very fleeting discomfort lasting one second or so.