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: Shares of 3D Systems (Nasdaq: TDSC) were down as much 11% today after a strange late afternoon dip. Volume was more than triple the normal amount.

So what: The shares were just toddling along, minding their own business, up slightly for the day. Then around 2:45 they began to fall, eventually hitting a low of $23.10. There is no news out that would indicate what happened to the 3-D printing specialist. The stock steadily recovered after the dip and closed the day down only about 3%.

Now what: Related companies like Stratasys (Nasdaq: SSYS) did not exhibit similar behavior. Perhaps a mutual fund or institution was selling off some shares of 3D Systems, but we have no way of knowing right now. As always, we caution investors not to react to random, no-news events such as this.

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Fool analyst Rex Moore owns no companies mentioned here. Stratasys is a Motley Fool Rule Breakers selection. 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.