Just press the flag.
This is to teach FIFO (transmission buffer) concept to kids. Cat feeds new data to FIFO buffers when they become empty. Crabs pick up data at the top of FIFO and delete it. Then they carry away it. FIFO is valid to avoid their work stopping. これはFIFO（転送バッファ）をわかりやすく説明するデモです。ネコがデータを転送バッファに積み、カニ達がそれを持って行きます。FIFOは、彼らの仕事が停滞するのを回避できます。
