Ash from Mt. St. Helens. Although it looks harmless if an animal breathes ash it can puncture their lungs. 

Reticulite is a special pumice where so much gas was trapped that the rock looks like interlacing bubbles.

Tephra refers to blocks and bombs, and smaller debris like scoria, pumice, and ash. As this becomes solidified as a rock it has unique chemical characteristics. 

Volcanic bombs ejected from a violent eruption. Imagine a bomb falling 100 feet on your car! Not a pretty picture. 

The volcanic rock has a vesicular texture, meaning that it is "holey". 

Rhyolite all swirled up with obsidian. This looks like a violent eruption.