Ten seconds to change your mind, no discrimination at all — it swallowed five crawlers, a city boss and a yard's awnings.
Riding up the Mindaro Line, Carl kept the scoop running the whole way and learned its limits. Switching a portal from one destination to the other takes a good ten seconds, during which it is off entirely and the cart is vulnerable, so every change of mind is a gamble. Watching for the blue dots of crawlers ahead is the only way to avoid sweeping up the people you came to save.
It failed both ways in one hour. At station 432 Carl saw the dots in time, cut the throttle and made the switch to Station and Repair Hub E — then plowed through five crawlers running full-tilt away from his headlight, one of whom got an ice bolt off into the portal, and teleported all five to a trainyard they had no reason to expect. Minutes later, outside Station 433, he hesitated over the switch when a blinking crossing gate appeared, hit it, and with one mighty thwum fed the entire Station Mimic city boss through the same doorway.
Elsewhere it did exactly what it was built to do. A flipping cart at Trainyard M dragged the yard's whole awning system into The Abyss before the portal shut itself off automatically; the Trainyard H cart wedged itself against a cavern wall with its portal still live and, thankfully, did not teleport away the cave system. The scoop remains the most powerful and least discriminating tool the party has: whatever touches the edge goes, like a strand of spaghetti, and it does not ask what it was.
A shimmering portal frame filling the nose of a rail cart, tuned to the abyss or a trainyard, shutting itself off automatically when the cart overturns.
The rescue's engine and its liability — a portal blade that teleports anything it touches, friend, foe or architecture.