Board Thread:General Discussion/@comment-5188108-20130331210748/@comment-1038387-20130404220310

Ratrangerm wrote: There was a clue from Bloodlines that something could happen to Wally, as it was revealed he was slower than the others and, when Neutron first went "boom" that Flash and Impulse had to carry Wally along because he was too slow to escape the explosion.

Technically, that Wally was slower was revealed way back in "What's the Story?", and then reiterated in "Common Denominators" (which, granted, shipped less than a week before "Bloodlines" aired.)