The healer has a unique texture. The red plus or cross represents health, or first aid. The blue diagonal line in the top left corner represents water. The orange diagonal line in the top right represents fire. The brown diagonal line in the bottom left corner represents earth, and the clear/transparent represents air.
The green zig-zag lines represent life/growth (Like plants: Photosynthesis). These are the elements we need for life.
The block heals you 1/2 a heart per click. It also is blast resistant to any amount of TNT. In versions before Beta 1.8, this block heals you to full health. Also in versions before Beta 1.8, the crafting recipe was different and easier to get this block.
When first added, the code to heal you wan't looked through, since MCE wanted to make sure he could get a semi-transparent texture to render right.
Once MCE got the texture to render right, he wanted to see what it would do if he clicked it. When he did, it killed him. He was in creative mode when he did this.
The healing code was taken from the crafting table, and changed a bit.
The texture actully has a meaning behind it, take a look at the top to see.
This has been the "iconic block" for the mod, but it has now been reaplced with the core reactor.