He had filled his bottle with water from the basin.
Once his bottle was full of basin water, he drunk some of it.
Immediately, he felt a tingle in his toes.
And he hardly noticed that his ears had slightly shrunk.
"Wow." Richard Reed said. "That water's very fizzy, but at least it's suitable for drinking, and it's sugar free."
Without a second thought, he filled up his bottle again, put his bottle in his jogging backpack, and resumed his jog.
But he hadn't noticed the plaque on the basin of the Fountain of Size, which read: 'THE WATER IN THE BASIN CAN AFFECT BODY PARTS, BUT IT WILL BE RANDOM. WHATEVER HAPPENS, THE EFFECTS COULD BE EITHER SHRINK OR GROW. BE AWARE OF THE RANDOMNESS.'
Since Richard Reed had drunk the water from the basin, it meant that a random part of his body would either shrink or grow, whenever he had a drink.
He didn't get far before he began to feel thirsty, so he had another drink from his bottle. And then, a random part of his body began to change size.