Mochlus brevicaudis — Short-tailed Writhing Skink
Some other names for this species:
Greer’s Writhing Skink
Some websites (e.g., lists in Wikipedia) spell this Mochlus brevicaudus, but this seems to just be a typo that has been inadvertently propagated.
I found this squirmy skink under a hunk of tarp that had apparently been left behind from some past field experiment. Dr. Adam Leaché identified it as Mochlus brevicaudis.