Glass - or heavily reinforced plastic - is a wonderful thing. Thanks to glass we've got, um, spectacles, see-through boat bottoms and The Gherkin. All good things.
This material of materials has also prevented a lioness from eating a toddler dressed as a zebra in its time, and now, from the looks of the video above, it's stopped a minor squabble between a dog and a penguin at an otherwise serene zoo.
Or maybe, if you squint your eyes a bit, they're just trying to play. Or perhaps, if you squint your eyes slightly less, the dog is just scrabbling at the glass and the penguin is staring at him, laughing.
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It's all up for interpretation, really - aside from the fact that it's really rather cute. That goes without saying.