Is this joke humorous or not? please comment

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A Dentist's Wisdom A man went to the dental surgeon to have a tooth pulled. The dentist pulls out a freezing needle to give the man. "No way! No needles! I hate needles!" the patient said. The dentist starts to hook up the laughing gas and the man again objects. "I can't do the gas thing - the thought of having the gas mask on is suffocating to me!" The dentist then asks if the man has any objection to taking a pill. "No,"- the patient says, -"I am fine with pills". The dentist then returns and says, "Here is a Viagara tablet." The patient says, "Wow - I didn't know Viagara worked as a pain pill!" "It doesn't,"- said the dentist -"but it will give you something to hold onto when I pull out your tooth."