"Making rubber gloves" joke

A dentist I know recounts sharing this story with an elderly lady, just as he was putting on his rubber gloves:

"Do you know how they make these rubber gloves?"

She said, "No."

"Well," he spoofed, "down in Puerto Rico they have this big building set up with a large tank of latex, and the natives walk up to the tank, and dip their hands in -- and then walk around for a bit while the latex sets up -- then they peel off the gloves and throw them into the big' Finished Goods Crate' and go around again."

She didn't laugh a bit.

Five minutes later, during the procedure, he had to stop working on her teeth because she burst out laughing.

She explained, "I just suddenly thought about how they must make condoms!"