The "stock" exterior shots of the house in Torrance are missing the "1630" address of Buffy's house and have the "1313" address of the actual house visible, while the exterior shots specific to this episode have "1313" removed or obscured and "1630" in place. (This is pervasive through all seven seasons of the series.)
There's no way Willow could have done a chemical analysis on the cookie Xander was eating just by looking at a few crumbs under a microscope.
When Buffy goes to unlock the front door in the beginning, it is clear that she doesn't even attempt to unlock the door but merely pushes the door open with the key.
As Buffy is investigating the house when the front door is open, she hears a glass shatter and Joyce says "No" quite audibly, but less than a second later when Buffy comes into the kitchen, Joyce is already kissing Ted.
When Ted gives Willow her computer upgrades, he hands her a stack of old floppy drives. Buffy was set in 1998, and floppy drives were already becoming obsolete with CD's coming in as the common replacement.