Slugs and snails in bait-stations

One of our rat baiters offers this advice to those whose bait-stations are visited by slugs and snails, and bodies need to be disposed of.

He recommends:
“Kill all slugs and snails that have ingested the rat bait and leave them in the box; the rat will then eat them.
If you discard the slugs / snails on the open ground, you negate the objective of protecting birds etc. - you risk killing them as well!
Same goes for cleaning out the trap with rat bait crumbs that accumulate in the trap.”

He offers a photo showing the dye from the bait in a slug cleared from a bait station.