When the Doctor explains that he and Susan are not of the human race, the wall behind them is clearly only a picture that has folds (possibly a large sheet).
After entering the TARDIS the top of the set is visible above and behind Ian as he says "you can't keep us here."
After Barbara and Ian enter the TARDIS, a boom mic is visible above Ian as Barbara says, "maybe we should leave now."
When Barbara says she and Ian should leave the TARDIS, a boom mic can be seen above Ian.