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King Digital Entertainment PLC (NYSE: KING) seems to be running on up and up, and shares are back near a post-IPO high. Monday’s gain was massive, up at 14.5% at $20.45 in late-day trading.

The question to ask is what to make of this latest move. It isn’t a just a volatility alert. This is now a serious volume spike alert!

Investors have made money betting on Zynga Inc. (NASDAQ: ZNGA), but only if they caught the bottom around $2.75 or so. That stock is now at $3.23, but its stock briefly went to $14 in early 2012 after its IPO. Let’s just say it has been a rough ride ever since – with 2013 sales falling to $873 million from $1.28 billion in 2012 and $1.14 billion in 2011.

Zynga’s market cap is $2.86 billion now. King’s is listed as $6.4 billion. Sterne Agee tried to address the volatility here. The firm’s Arvind Bhatia, who rates the gaming company as Neutral, said in an intra-day report:

While we haven’t been able to identify a concrete reason for the stock’s 22% appreciation in the last two trading sessions, our best guess is it may have been triggered, at least in part, by end-of-the-quarter short covering and in part by positive sell-side commentary. This is a heavily shorted stock (10.8M shares or nearly 50% of the float is short) with a short-interest ratio of 13 days.

Bhatia also said that King’s rise may be tied to the recent rise in shares of a smaller competitor — Glu Moble Inc. (NASDAQ: GLUU) — now above $5 from under $4 last week. That gain is based upon the release of its Kim Kardashian: Hollywood title.

After seeing this sort of run, it feels like a chat room run from the old day trader days a decade ago. Anyhow, volatility is an understatement for shares having risen from $17 to over $20.80 in just two trading sessions when no news has been released by the company.

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As for the King Digital volume spike, the stock hit 5.9 million shares by 2:30 p.m. ET (with 90 minutes to close, plus after-hours). Average volume is 1.31 million shares. Volume was almost 3.5 million shares on Friday, but Monday’s volume is the highest reading since the 6.75 million shares traded back on May 7 and then again since the first and second day this stock ever traded from the March IPO (41 million on March 26 and 8.4 million on March 27).