“Doctor, don’t! It could be a trap!” Martha tried to pull him back, but the Doctor shook her off.
“Course it’s a trap; I already knew that.”
“So don’t go!”
“Because you’ll be captured!”
“Will I? Funny thing about traps; when you know they’re there, when you know what they are, sometimes, if you’re very clever…” The Doctor aimed his sonic screwdriver at a few key points. “All it takes are some minor alterations and you can turn a trap against whoever set it.”
Before the Sontarans knew what was happening, they were caught in their own trap.