Your undead form ignores the limits of mortal physiology.
Benefit(s): You are treated as one size smaller for the purpose of calculating penalties for squeezing, and gain a +5 competence bonus on Escape Artist checks. If you possess 10 or more Hit Dice, this bonus increases to +4.
Pathfinder Roleplaying Game Monster Codex © 2014, Paizo Inc.; Authors: Dennis Baker, Jesse Benner, Logan Bonner, Jason Bulmahn, Ross Byers, John Compton, Robert N. Emerson, Jonathan H. Keith, Dale C. McCoy, Jr., Mark Moreland, Tom Phillips, Stephen Radney-MacFarland, Sean K Reynolds, Thomas M. Reid, Patrick Renie, Mark Seifter, Tork Shaw, Neil Spicer, Owen K.C. Stephens, and Russ Taylor.