One way to hold spurt: something was shut in, it found a small opening, and it got out fast. Water behind a crack in a pipe, flame behind a hole, blood inside a cut. What comes out is a narrow jet rather than a wide flow, and it is over almost as soon as it starts — or it comes again in short bursts. English then takes that shape off the water and puts it on speed, effort, temper and even a child's height: flat for a while, one sudden jump, then flat again.
From the word’s history
The Wiktionary entry supplied in this packet traces spurt to earlier spirt or sprit, meaning to sprout, from Old English spryttan, and further back to a root meaning to strew or sprinkle. Sprouting is itself a sudden push out from inside, which sits close to the modern jet of water.
這份資料裡的 Wiktionary 記錄，spurt 來自更早的 spirt／sprit（發芽），再往前是古英語 spryttan，最遠可追到一個表示「撒、播」的印歐字根。發芽本身就是從裡面一下子頂出來。這條線索跟今天「噴出去」的畫面是同一個動作，只是一個是芽，一個是水。
Wiktionary entry supplied in this packet, source_ref kaikki:3f6f69a190036ae4:666586558 — "From earlier spirt, sprit ('to sprout'), from Middle English sprytten, from Old English spryttan… from Proto-Indo-European *(s)per- ('to strew, sow, sprinkle')."
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