Inside the lodge, The Doctor's hat can be seen on the back of the chair by the grandfather clock. Every time The Doctor enters/leaves the lodge the hat remains on the chair. Yet in all of the outdoor scenes (except inside the poacher's hut) The Doctor is wearing his hat.
The Doctor chides Sarah Jane for throwing the box with the gelignite, stating that "Sweating gelignite is highly unstable." Gelignite can "sweat" (i.e. leaching out nitroglycerin) but it is completely stable in the absence of a detonator.