Although he agrees that it would take a force of about 3,000 newtons to push over a standing cow, biologist Steven Vogel thinks that the study by Lillie and Boechler overestimates the pushing ability of an individual human. Using data from Cotterell and Kamminga, who estimated that humans exert a pushing force of 280 newtons, Vogel suggests that someone applying force at the requisite height to topple a cow might generate a maximum push of no more than 300 newtons. By this calculation, at least 10 people would be needed to tip over a non-reacting cow. However, this combined force requirement, he says, might not be the greatest impediment to such a prank. Standing cows are not asleep and like other animals have ever-vigilant reflexes. "If the cow does no more than modestly widen its stance without an overall shift of its center of gravity", he says, "about 4,000 newtons or 14 pushers would be needed—quite a challenge to deploy without angering the cow."