"Take a sip and trust your gut," The man with the mustache said. "If you think you're in need of a bit of luck." As a general rule, Harry didn't trust strangers, or the things they tried to give him, but he really needed to find Aunt Petunia.
Harry and Dudley are attacked one evening, and Snape is called to fix it. A child sized Harry, who looks much more like Lily than James at this age, was not what he was expecting.