“Oh, don’t worry about them,” the Doctor said airily. “You’ll soon get used to the wildlife here.”
“Wildlife?” Rory stared in disbelief at what looked to be a small avalanche of pebbles somehow rolling uphill. “They’re alive?”
“Silica based life forms. They’re mostly harmless, travel in herds. Try not to tread on them though.”
“Why not? Would it hurt them?” Amy asked, crouching down to get a closer look at the herd of pebble creatures.
“Them? No, but it wouldn’t do your feet much good; they’re not very comfortable to step on, hard and lumpy.”
“I’ll keep that in mind.”