Police may also feign kettles in order to cause a protest to disperse.
Protests that move quickly are harder to kettle (but are easier to split up as people get left behind). Something important to note is that kettles are used by police to gather intelligence. Police may tell you that you will be allowed to leave if you provide your name and your address, if you give information about other protestors etc. Police can and will lie to you, do not trust them. Never talk to cops. Being trapped in a kettle is stressful. Police may decide to arrest a few of you or all of you. Their goal is to gather information and to demoralize you. They might threaten or harass you. Your goal should be to remain calm and to help the people around you remain calm. Remember if nobody talks, everyone walks.