Believe it or not I believe it's a sign of dehydration.

Raise the "AMBIENT" humidity as high as you can. This does not mean saturate the substrate. Make a water/soak dish available that he can easily walk into and out of.. about chin deep. [ I'm not big on "force-soaking" ] Place your redfoot into the dish 3-4 times a day and let him decide what he wants to do. And spray him 'til-he-drips' always.

Of course diet is important as well as a place to hide.. they don't bask much at all.

If yours IS sitting under the light it's either trying to thermo-regulate ( he's too cool ) or he needs calcium/D [ which they normally acquire thru their diet in the form of animal protein, fungi and feces ].

Redfoot tortoises are quite unique with their needs.

-----
Terry E. Kilgore
Turtletary.com