Jesus said the Son of Man must be lifted up, just as Moses lifted up what in the wilderness?

Answer: The snake

Recalling the snake Moses lifted up in the wilderness, Jesus said the Son of Man must be lifted up so believers have life.

“Just as Moses lifted up the snake in the wilderness, so the Son of Man must be lifted up, that everyone who believes in Him may have eternal life.”— John 3:14-15 (BSB)