How science can make our buttons better

Keith Lang, an Australian software developer and UX Designer has a great talk about The Science of Aesthetics and how it pertains to UX design.

The section pertaining to the concept of synesthesia (a sensation produced in one modality when a stimulus is applied to another modality) is particularly interesting. Spiked objects evoke a certain internal warning bell in people and he's conceived a simple way of implementing this is in button design. I would love to see some real world implementations of his example:

Which do you find more effective?

I highly recommend checking out his entire talk here: The Science of Aesthetics.