shrewd innocence?

the sitename for this blog came from a picture I saw that had a snake and dove drawn in pencil, and theres a banner that says:

"wise as serpents innocent as doves"

and that is something Jesus called His disciples to be in Matthew 10. I found the word shrewd in a different translation. I love it because it's hard to be both of those at the same time while witnessing. It's very easy to be innocent when it comes to witnessing; being shrewd is harder for us because it doesn't seem like a very winning strategy. But, earlier in the passage, Jesus told them to go witness to the lost sheep of Israel, not just the Gentiles. He wanted them to be shrewd and innocent, strategic in witnessing and above reproach.

so yeah i just wanted to explain the whole "shrewd innocence" thing.