Fig 1.

Traction forces exerted by an MDCK monolayer upon its substrate in the direction perpendicular to the leading edge. Spatial distributions of tractions are heterogeneous, and extreme mechanical events (cells generating very large tractions such as those pointed by arrows) are frequent both at the leading edge and many rows behind it. The circle encloses one of the many cells that appear to be pulling the “wrong” way. Adapted from [17] with permission from Nature Physics.