Chris posted a picture of the two of them recently, and it also happens to be a full-body shot of Blobbo, something you don't see often:
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Comparing that to the older picture, it does look like he isn't as rotund as he was whenever that was taken, but everyone immediately focused on what the fuck is going on with his legs. This led to varying speculation that this "weight loss" might not be because he's eating better and exercising, but because of other health problems eating away at his body. Coupled with his increasingly gray hair (when it isn't in the process of dying entirely), droopy jowls, and generally pained expression, Bob looks like he's at least ten years older than he is. All that overeating, booze, and unbridled rage is killing him, and he just can't see it.