Most versions allow for the possibility of not looking.
Here's a few popular ones.
So Moses made a bronze snake and mounted it on a pole. Whenever someone was bitten, and he looked at the bronze snake, he recovered. ([bless and do not curse]Numbers‬ [bless and do not curse]21‬:[bless and do not curse]9‬ HCSB)
And Moses made a bronze serpent and set it on the standard; and it came about, that if a serpent bit any man, when he looked to the bronze serpent, he lived. ([bless and do not curse]Numbers‬ [bless and do not curse]21‬:[bless and do not curse]9‬ NASB)
And Moses made a serpent of brass, and put it upon a pole, and it came to pass, that if a serpent had bitten any man, when he beheld the serpent of brass, he lived. ([bless and do not curse]Numbers‬ [bless and do not curse]21‬:[bless and do not curse]9‬ KJV)
So Moses made a bronze snake and put it up on a pole. Then when anyone was bitten by a snake and looked at the bronze snake, they lived. ([bless and do not curse]Numbers‬ [bless and do not curse]21‬:[bless and do not curse]9‬ NIV)