An apparatus comprising: a memory system storing a plurality of sequences, each sequence comprising data for reproducing a different pattern of interactions between a respective plurality of moving characters and storing a combination data structure defining for each sequence connectability of that sequence with other ones of the plurality of sequences; a processor configured to determine pair-wise combination of stored sequences, by selecting sequences for pair-wise combination that are defined as connectable by the stored combination data structure, wherein each pair-wise combination has in common at least one of their respective plurality of moving characters and configured to use determined pair-wise combinations of the stored sequences to produce and output video graphics comprising a series of sequences in which movable characters repetitively interact in different combinations.