Amos Diggory's head was sitting in the middle of the flames like a large, bearded egg. It was talking very fast, completely unperturbed by the sparks flying around it and the flames licking its ears.
Effect: communication between fires
Using Floo Powder in a fire connected to the Floo Network, a person can communicate with another over distance. The head of the person making contact appears in the midst of the flames and they can hold a conversation and even interact physically with the person they are connecting to.
References from the canon
- Amos Diggory used this method of contacting Arthur Weasley when the fake Moody reported being attacked (GF11).
- While in hiding, Sirius Black talked to Harry by means of a wizard fireplace (GF19).
- Snape used a powder thrown into the fire to contact Lupin and ask to speak to him (PA14).
- When the Ministry wanted to spy on all communication in and out of Hogwarts, they employed the Floo Regulation Board to monitor the Hogwarts fires (OP27, OP28).
- Harry took a risk and spoke to Sirius, Lupin and Kreacher through the fireplaces at Hogwarts anyway (OP28, OP29, OP32).
In the Order of the Phoenix movie, Sirius Black was depicted in the fireplace as if his head was a pile of burning charcoal.