Snakes are where?

Yesterday Matthew was going outside to walk his playdate home. I told him to check the mail on his way back. He comes back a few minutes later... no mail. Here's our conversation....
Me: "Matthew, where's the mail?"
Matthew: "You said NOT to check the mail."
Me: "Matthew, why would I tell you NOT to check the mail?"
 Matthew: "In case there were snakes in the mailbox."

Me: "........"