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When predators rely on high-speed movements to capture prey, prey often exhibit traits that result in correspondingly extreme physical performance. Biomechanical studies of these interactions are typically conducted in laboratory settings, thereby eliminating some of the ecological context. We studied how behavioural state, specifically vigilance level, of kangaroo rats affects evasion performance during simulated rattlesnake strikes. Vigilance levels were manipulated through the presentation of a tethered sidewinder rattlesnake. After predator exposure, we recorded kangaroo rats evading simulated attacks, and the videos were used to extract information about kangaroo rat performance. High-vigilance kangaroo rats (recently exposed to a rattlesnake) significantly outperformed low-vigilance kangaroo rats (not exposed to a rattlesnake) in both reaction time and take-off velocity, and executed steeper jumps. Although our recordings were not adequate for detailed biomechanical quantification, reaction times of high-vigilance kangaroo rats may be among the fastest recorded for mammals, with 36% of these individuals producing a visible response to attacks within no more than 8-17 ms and a group mean of 23.1 ms. This study demonstrates that behavioural state can have major effects on performance during predatory encounters. Therefore, under some conditions, laboratory studies of evasive anti-predator manoeuvres may underestimate performance in the wild.