Harry Kane, England’s captain and the World Cup’s leading scorer, has at times appeared more interested in rinsing his mouth with fluid than swallowing it during the tournament.

Late in an epic second-round match against Colombia that extended through 30 minutes of added time and penalty kicks, Kane vigorously squirted his sports-drink bottle into his mouth. Then he expectorated a geyser of fluid instead of ingesting it.

Other players on England, which faces Croatia in a semifinal on Wednesday, also rinse and spit during breaks as they tire late in matches and performance tends to decline. So have many players on other teams. Cristiano Ronaldo, the Portuguese star, took swigs from his bottle and expelled the drink in dots and dashes in a kind of aquatic Morse code.

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Some players may want to avoid feeling bloated and are simply refreshing their mouths in the heat. But others appear more deliberate and purposeful. Players are notoriously cloistered during the World Cup and are especially loath to speak about their fitness secrets, so the contents of their bottles are not known. But they may be employing a technique called “carb rinsing” or “mouth washing,” according to some exercise and nutrition scientists.