  Swimming cells and microorganisms are a critical component of many biological
processes. In order to better interpret experimental studies of low Reynolds
number swimming, we combine experimental and numerical methods to perform an
analysis of the flow-field around the swimming nematode Caenorhabditis elegans.
We first use image processing and particle tracking velocimetry to extract the
body shape, kinematics, and flow-fields around the nematode. We then construct
a three-dimensional model using the experimental swimming kinematics and employ
a boundary element method to simulate flow-fields, obtaining very good
quantitative agreement with experiment. We use this numerical model to show
that calculation of flow shear rates using purely planar data results in
significant underestimates of the true three-dimensional value. Applying
symmetry arguments, validated against numerics, we demonstrate that the
out-of-plane contribution can be accounted for via incompressibility and
therefore simply calculated from particle tracking velocimetry. Our results
show how fundamental fluid mechanics considerations may be used to improve the
accuracy of measurements in biofluiddynamics.
