Idiom Definition:
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"to be on your toes"
to be very aware of a situation and ready to react quickly
Synonyms:
active, bright, cagey, circumspect, clever, conscientious, fast, heedful, intent, intelligent, mindful, observant, guard, perceptive, quick, ready, sharp, studious, vigilant, wary, watchful, wide-awake, wired, wise