The cop needed a paramedic, not Charlie. So, he reached out his hand and tried to touch someone who passed by, so he would hop into their body.
But, unfortunately, as he did, the sky flashed green. And when he actually grabbed someone's hand, nothing happened.
He was stuck as the paramedic.
"Larry, what hell are you doing?" the other paramedic repeated.
Charlie wasn't a paramedic. He couldn't save the cop's life. What was he going to do?