You can just imagine what kind of bad wise cracks this guy is full of so you remain silent as he steps away. After a few paces he turns again.
"I'm going to leave you here in the dark, tied to the tree, alright?" he says. His head is tilted to one side as he awaits a response.

You shrug in response and slowly shake your head from side to side

"Mlhm ee," you say around the gag the best you can.