The Wendigo is a mythical creature appearing in the mythology of the Algonquian people. It is a malevolent cannibalistic spirit into which humans could transform, or which could possess humans. Those who indulged in cannibalism were at particular risk and the legend appears to have reinforced this practice as taboo.
The first time that one of the sisters (Piper) turns into something evil.
While AB- may be a more rare blood type, an individual can receive blood from any other individual with a negative blood type (AB-, A-, B-,O-)
Phoebe was searching the Web (around 18:40) and apologises to Prue that she tied up her phone lines. This implies that she was using a dial-up connection using the normal voice phone line, with a maximum data download rate of 56kb/s, although it might have been as low as 0.3kb/s, and upload speeds could be as low as 75b/s. So, the Halliwells are still on dial-up access, about to be superseded by broadband internet connection. Only just entering the modern world.