1. A method comprising the computer-implemented steps of: while a plurality of users are participating in a conversation that is being carried out using a corresponding plurality of messaging clients that belong to a messaging system, receiving input that was submitted through an interface provided by one of the messaging clients involved in said conversation; in response to the input, causing at least one of the plurality of messaging clients to generate a visual image that exhibits at least one of: a behavior that is based, at least in part, on information obtained from a service external to said messaging system; a behavior that causes the visual image to change position relative to other previously-displayed elements of the conversation; a behavior that is based, at least in part, on the presence of one or more other elements on a display screen on which the at least one messaging client is displayed; a behavior that is based, at least in part, on results produced by a pseudo-random number generator; a behavior that is affected by user input received through an input device of a computer upon which said at least one messaging client is executing; or a behavior that is based, at least in part, on information maintained by said messaging system about a user from whom said input was received.