Distribute index cards to each participant. Ask the participants to write a little-known fact about themselves and keep it hidden from the others.
Divide the participants into two equal-sized groups. Collect the cards from one group (called the confessors) and give them to the other group (called the inquisitioners), one card per participant, with the written side down. Warn the inquisitioners not to read the statement in the card they received.
Ask all participants to stand up. Ask the inquisitioners to hold the index card against their forehead with the written side showing. Make sure that the inquisitioner holding the card is not able to read it, but everyone else is able to. Ask the inquisitioners to walk around the room, asking different confessors whether the card belongs to them.
If a confessor sees her card, she has to say "Yes". Once an inquisitioner has tracked down the correct confessor, she asks a series of Yes/No questions to discover the exact nature of the LKF. The confessor responds truthfully but limits her responses to "Yes" or "No".
The question and answer session continues until the inquisitioner discovers the LKF. She verifies her guess by reading the statement on the card, places the card on top of her head, and walks around the room in search of someone else holding a card on top of her head. Participants with the cards on tops of their heads swap cards with each other (without reading the LKF on the card) and repeat the search-and-question process all over again.
Conclude the first round of the icebreaker after a suitable period of time. Repeat the activity by collecting the original LKF cards form the inquisitioners and giving them to the confessors. Switch the roles of the participants and replay the icebreaker.
Source: Thiagi Group - David Scott