willing

predisposed, prone

accommodating, agreeable, compliant, cooperative, obedient, obliging, submissive

favorable, receptive

prepared, prompt, quick, responsive, swift

desirous, eager, enthused, enthusiastic, excited

receptive, responsive

immediate, instant, instantaneous, summary

breakneck, breathless, brisk, fast, fleet, fleet-footed, hit-and-run, lightning, rapid, rapid-fire, rattling, snappy, speedy, swift, whirlwind

eager, keen, sharp

apt, clever, quick, quick-witted, ready-witted, sharp-witted, smart

discretionary, elective, optional

impulsive, instinctive, spontaneous, unpremeditated

conscious, deliberate, intentional, knowing, willful (or wilful)