Ya know Wired Science writer Erik Klemetti brings up an excellent point, which I hadn't thought in the context of video games previously.

Lord help if you fell on Lava, but chances are you wouldn't really sink into it.

from: http://www.wired.com/wiredscience/2011/12/the-right-and-wrong-way-to-die-when-you-fall-into-lava/

Molten lava is nothing like water. Sure, everyone thinks that liquid rock (magma) is going to behave like any other liquid (e.g., water), but there are some key physical properties that tell us it just isn’t the case. Let’s compare!

• Water has a density of 1000 kg/m and a viscosity of 0.00089 Pa*s.
• Lava has a density of 3100 kg/m and a viscosity of 100-1000 Pa*s....

Do you suppose throwing yourself into lava would have the same effect as falling into a lake? Probably not. The average human has a density of ~1010 kg/m, so a little bit more dense than water.....If you are less than one-third the density of basalt (and you are, admit it), it is going to be next to impossible to sink into that liquid.

This is going to bug the crap out of me now every time I see something like this