rattleback » rattle + back » tap + spine » Spinal Tap

Rattleback (a.k.a. wobblestone, celt)

http://en.wikipedia.org/wiki/Rattleback

http://demo.physics.uiuc.edu/LectDemo/descript/1148/rattleback.wmv

(online demo)

(Rattlebacks are widely available through online science stores such as Edmund Scientific.)

Spinal Tap (Critically lauded mockumentary film of 1984 directly by Rob Reiner whose full title is This is Spinal Tap. But the film is familiarly known as just Spinal Tap.)

http://en.wikipedia.org/wiki/This_Is_Spinal_Tap

http://www.rottentomatoes.com/m/this_is_spinal_tap/

(reviews)