Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What's happening: Following a 10% pop yesterday, shares of Lumber Liquidators Holdings Inc. (NYSE:LL) were up another 15% as of 11:45 a.m. Wednesday after an activist investor revealed a significant stake in the company.

Why it's happening: Specifically, Chapman Capital CEO and activist investor Robert Chapman told CNBC he has taken a long position in Lumber Liquidators equal to around 15% of his entire hedge fund. Chapman also noted that position was opened partly through call options, and is set to discuss the move with CNBC later today. 

For perspective, yesterday's initial jump came after Lumber Liquidators provided an encouraging outline for its upcoming business update conference call, which helped ease investors' concerns of receiving additional bad news following a recent negative 60 Minutes report. That report alleged Lumber Liquidators' products violate California Air Resources Board regulations due to high levels of formaldehyde, a known carcinogen -- though Lumber Liquidators has consistently disputed the claim and insists its products are safe. Also yesterday afternoon, hedge fund BlackRock disclosed in an SEC filing it has more than doubled its stake in Lumber Liquidators to 2,737,622 shares, or 10.1%, up from 4% at the end of 2014.

To be sure, if Lumber Liquidators manages to prove 60 Minutes' report was off-base, these bets could pay off big with shares still down over 50% since the report was released. For now, that's why patient investors would be wise to listen closely to what the company says during tomorrow's conference call.

Steve Symington has no position in any stocks mentioned. The Motley Fool recommends Lumber Liquidators. The Motley Fool owns shares of Lumber Liquidators. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.