The plain yellow snail in the video is actually a Banded Snail, in one of the species' many colour forms. Seconds before this video it was behaving very strangely, waving its shell from side to side as if to dislodge something. A fly had been circling it and occasionally landing on it so perhaps it was to do with that. If any of you know what might have caused this behaviour please get in touch with me (firstname.lastname@example.org). Needless to say as soon as I started filming the snail behaved normally.
The only other video I have of a snail is this one from years ago showing a Garden Snail speeded up.