There is another street evangelist named Pete Cabrera Jr. who has vids on Youtube; I'll get the link up in a few.
Anyways, he was demonstrating the Kingdom of God to this athiest guy in a pub somewhere in the UK, and Pete was commanding the guy's leg to grow out, and return, etc. It was doing as he commanded it. After a minute of that, he told the athiest guy to speak to it and try it, and he did try and nothing happened. It looked like he kinda freaked because of this, but it was clear to him that God had power flowing through Christians, as opposed to unbelievers. The guy ended up getting saved. Praise God.
Anyways, there's another example of what I responded with.
EDIT: Here's a relevant scripture -
"And these signs shall follow them THAT BELIEVE; In my name shall they cast out devils; they shall speak with new tongues; They shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover." - Mark 16:17-18 KJV