When the Marshmen pick up and carry the TARDIS away, the camera tilts and the actors inside lurch from one end of the console room to the other (a la 60s Star Trek) to show this. However the loose objects in the room (coat stand, knife, etc) don't do this and simply fall to the floor revealing it to simply be a staged effect.
When the TARDIS is being carried away, Tylos drops his knife as he and the other characters lurch to the far end of the control room to show the ship is being tipped on its side externally. But the knife does not slide along the floor with him, suggesting the actor dropped it by accident.
As the Doctor wanders the corridors of the Starliner, a blue screen (with no superimposed background) is clearly visible at the back of one of them.
Romana surmises that the Marshmen are going to use the TARDIS as a battering ram against the Starliner by throwing it down a ravine. If the TARDIS was light enough for the Marshmen to carry into the cave, it wouldn't even scratch the outer hull of the Starliner. It would be like throwing a pebble at a tank.
Romana states that the TARDIS weighs 5 times 10 to the power of 6 kilos - (put mathematically is 5x(10^6)=5000000) This would be 5 million kilos, which the Marshmen couldn't possibly lift up. Nor would it be able to land in most of the places it does throughout the show's history. It has been implied previously that the TARDIS just weighs the same as a typical police box as it has been moved by humans before.
In the final scene, Adric challenges the other youngsters after they closed the TARDIS doors while Romana is still outside in the cave. But he just slammed the exterior doors shut himself.