Using a repeating command block while your character is surrounded by a ring of blocks to keep your character from moving while summoning in cows into a smallish pen via a repeating command block will cause minecraft to stop responding within a relatively short period of time due to minecraft trying to handle more than 247 sounds at one time, and thus preventing you from doing anything, including shutting the command block off.

Console continues to log warnings and info even AFTER the game has been force closed.