*The total price includes shipping fees which typically cover an entire order, making it more economical to purchase multiple medications in the same order.
As Voldemort Disapparates, they came out of the woodwork and Harry and Snape exchange an understanding look, Harry gathering Snape's memories that poured from him as he died there from Nagini's poison. Snape was bitten in the neck, not snake food or Snape wouldn't have lasted long enough to give Harry his memories. Nagini did not come out of her floating magic ball. The ball rolled onto Snape as the upper half of his body was contained in it. I don't think Harry and Snape exchanged understanding looks. Harry was shocked and Snape was bleeding to death.
First, a purely practical reason - he needed Harry to believe him. The emotional connection to Lily is crucial to understanding why Snape and Dumbledore did what they did. Snape can give what happened, but to truly convince Harry, he must also give the why.