Liquid already knew... (spoliers)
that the foxdie in Snakes blood was going to turn him old? I was playing this (MGS2) the other day and during the part when Liquid takes over Ocelot he mentions snake only having a few years left, and how they took the samples from Big Boss when he was in his 50's and that liquid could live on thru Ocelot... so I'm assuming that was the foreshadowing for what happens to Snake in MGS4?
"Self Improvement is masturbation, self destruction is the answer."