Or, at the least, in the case of the pig, it’s the fatal one.
Quickly severing the carotid, the erupting blood caught for use later in black-pudding or similar, this ensures a (comparatively) quick and painless death — although not necessarily a silent one.
This is a commercial guide to the cuts of meat made by the butcher, post-mortem, but it’s a visually colourful and useful one nevertheless.