What is the Tender Trap? It's what happens when someone places the tender of a toy or model locomotive backward because it "looks right that way." Usually, to do so, they have to ignore the connectors that are specifically designed to work only when the tender's facing the right way.
So to insist on placing the tender backward, ignorance isn't enough -- you have to deliberately ignore the evidence in front of you.
One doesn't expect a lot from a 1950s monster movie. But The Black Scorpion did something that I believe is unique among B-movies. It fell into the Tender Trap.
The 1957 movie was a joint American-Mexican production, and clearly with an eye always to the bottom line. The trailer can't quite disguise all the shortcuts. Even in this two-minute promo, there's a lot of stock footage (even more in the film). While the stop-motion is well done, it's sometimes undercut.
Did you notice the train wreck? Here it is in detail:
The special effects department used a Lionel train set. That wasn't uncommon at the time. But they didn't have the budget (apparently) to repaint it!
And... the tender's backward. In order to connect the tender, the special effects crew had to wire the tender's knuckle coupler to the locomotive frame, and wire the tender's coupling bar to the passenger car's knuckle coupler. Wouldn't it have been easier to just turn the darned thing around -- especially if time was money?