Arm in Guillotine choke.

[phenompromos]

Can anyone describe to me how to do it? It must be a pretty high percentage hold. Thanks!

[Tom Gavrilos]

I believe another name for it is a Peruvian Neck Tie.
Explain what you mean by High Percentage?...

[phenompromos]

By high percentage hold i mean it has i high rate of success when attempted.

[Ari Bolden]

Several variations (arm and head trapped) turn the normal guillotine into:
Anaconda Choke
http://www.submissions101.com/chokes7.htm

D'arce Choke or Brabo Choke
http://www.submissions101.com/chokes18.htm

Hope that helps a bit.
cheers
Ari