  Strongly lensed galaxies at high redshift provide a unique window into the
early universe. We compare the internal kinematics of the strongly lensed
Lyman-break galaxy (LBG) 'arc&core' at z=3.2 (the first strongly lensed z~3 LBG
with the signs of rotation on sub-kiloparsec scales) with an LBG that is not
gravitationally lensed, as well as with a larger sample of actively
star-forming galaxies at slightly lower redshifts. All galaxies have deep
rest-frame optical integral-field spectroscopy obtained with the VLT. The
unlensed galaxies appear to have a larger ratio of random to bulk motion. Field
galaxies also have broader lines than strongly lensed LBGs with rest-optical
spectroscopy, where spectra were extracted from regions with similar physical
size. To ensure observational success, studies of high-redshift galaxy
kinematics often focus on bright and luminous targets, and our comparison
suggests that this may lead to a serious bias.
