Steven, dressed as Mr. Knight in the white suit, takes off his white jacket and throws it on the ground with his right arm. When the shot changes to another angle, his throwing arm is his left.
Arthur Harrow is able to hear Steven/Marc's conversation in the back of the car through the walkie-talkie left active on the dashboard. Walkie-talkies require the transmit button to be physically depressed in order to transmit. Harrow wouldn't be able to hear anything said in the car unless the button was being physically held down. No one was holding down the button and there were no signs that the walkie-talkie had been jury-rigged to hold the button down.
For most of the first half of Layla's motorcycle-ride conversation with Steven, her mouth doesn't match her words.