Leo tells the sisters not to touch the darklighters arrow because the poison will kill them, however, in future Paige is the only sister who can not touch the arrow because it is only poisonous to whitelighters and Paige is half whitelighter.
In the bathroom scene, when Prue tries to shoot Alec with the crossbow, it goes through him and into the wall behind him. He orbs away and there is clearly no arrow in the wall behind him.
Right before Daisy returns to her room and Alec finds her, there is a shot of the Senator Hotel, revealing where she is staying. Later, when Internal Affairs questions Andy about finding the manager dead, they say, "Motel Capri."
When Piper is holding up Leo's dogtags, and putting them around her neck, the tags she is holding are modern day era. Leo is from WWII which used round tags. Later they switched to oblong-notched, and still later (modern) they switched to the oblong non-notched which she holds.
When Piper is holding up Leo's dog tags, and putting them around her neck, the tags she is holding are modern day era. Leo is from WWII which used more round tags and had a notch. Later ( they switched to more oblong-notched tags, and still later (modern) they switched to the oblong with rolled edges which were non-notched which she holds.
Leo always says he can't heal the dead. He is already dead when Piper finds the trigger to his power, but she's able to heal him.