Psywaves
Procrastinating Pedantic Perfectionist™
If Slurpuff's HP is an an odd number, then that'd be why it went down to 51% and hence didn't activate its Sitrus Berry.1st turn of the game. Sitrus berry did not activate after successfully using belly drum . This happened twice but I only got the replay of the second one. I noticed after using b drum. slurpuff lost only 49.8% of its hp that's why sitrus did not activate, I think because the hp was rounded "up" instead of "down" from 50% hp reduction of b. drum.
Replay: http://replay.pokemonshowdown.com/oususpecttest-197505056
edit: ninja'd