This is the Act part of the crime/ Physical element. E.g. Pulling trigger or punching someone.
Must be volountary meaning D is in control of his actions. Lord Denning gave a hypothetical theory showing automatism where the driver loses control because he get stung by swarm of bees, struck on the head by a stone or has a heart attack (Hill V Baxter)
Some crimes are 'being' rather than 'doing' E.g. Winzor, drunk in hospital removed onto high way. Held= Guilty for being drunk on the highway
This is another way of commiting the actus reus, normally actus reus requires positive act → Because we dont have a good samartian law
Ommisions is a failure to act