From The Angel Island Immigration Station Website.
"To counter this practice, Immigration inspectors developed grueling interrogations, and by 1910 they had refined this procedure. The immigrant applicant would be called before a Board of Special Inquiry, composed of two immigrant inspectors, a stenographer, and a translator, when needed. Over the course of several hours or even days, the applicant would be asked about minute details only a genuine applicant would know about — their family history, location of the village, their homes. These questions had been anticipated and thus, irrespective of the true nature of the relationship to their sponsor, the applicant had prepared months in advance by committing these details to memory. Their witnesses — other family members living in the United States — would be called forward to corroborate these answers. Any deviation from the testimony would prolong questioning or throw the entire case into doubt and put the applicant at risk of deportation, and possibly everyone else in the family connected to the applicant as well. These details had to be remembered for life. Because of return trips to China, the risk of random immigration raids and identity card checks on the street, a paper son often had to keep these details alive throughout their life."