Cum, most likely... not originally of course, but the original stuffing has no doubt been chemically converted over the years, saturated as it is with Zerosignalone's ejaculatory fluids, that it is now, for all intents and purposes, dried seminal discharge. This can bring to mind one hopeful thought: If Zero spends all his time impregnating Snoopy and Pooh Bear, at least there is no hope of an actual genetic offspring that would be any more dangerous than say, Spongebob Squarepants, albeit equally annoying!