Willow is talking to Tara and playing with a kitten. The kitten changes position and location while Willow is in mid-sentence.
At 20:03, when Buffy rolls down the hill into some rocks, it is obvious from the way they shift under the impact that they are lightweight, flat-bottomed props sitting atop a soft stunt mat. Then, as the camera revolves while looking down on Buffy, you can see a patch of reflected light move across a "rock" and onto her shoulder in time with the camera motion.
At around 20:26 Spike feigns being out of breath as he arrives at Giles' house despite having previously stated during the episode "Lovers Walk" "Not while I breathe. Actually I don't breathe."