My guess is that St. Thomas would had his mouth covered with both hands; Trembling and shut himself up.
You want to know why? Check this out:
Jesus said to his disciples, "Compare me to something and tell me what I am like." Simon Peter said to him, "You are like a just messenger." Matthew said to him, "You are like a wise philosopher." Thomas said to him, "Teacher, my mouth is utterly unable to say what you are like."
Jesus said, "I am not your teacher. Because you have drunk, you have become intoxicated from the bubbling spring that I have tended." And he took him, and withdrew, and spoke three sayings to him. When Thomas came back to his friends they asked him, "What did Jesus say to you?" Thomas said to them, "If I tell you one of the sayings he spoke to me, you will pick up rocks and stone me, and fire will come from the rocks and devour you." (The Gospel of Thomas, saying 13. Italics added)
Probably you are now guessing or dying to know what did Jesus said, right? I can't tell you because you will stone and fire will burn you!