The sound one makes when sneezing is natural, and involuntary.  Correct?

The answer is not exactly.  The sound one makes seems to be in large part a learned behavior.  The sound emitted is different around the world.  Achoo is common in English speaking countries.  Atchim in Portugese; Atchaum in French; Hatshi in German; Apchki in Russian; Hopsu in Greek and Turkish; Achhee in Hindi; Hat xi in Vietnamese; Eichi in Korean; Hakshon or hakashun in Japanese; Ha-ching in the Philippines (Don Lewis, The Surprising Story Behind the Sound of Sneezing, nowiknow.com; James Chapman, The Sound People Make When Sneezing Across the World, theuijunkie.com; Emma Tracey, Why Deaf People Sneeze Silently, bbc.com).

Moreover, the sound made by deaf people is noticeably different.  “British deaf people, particularly users of sign language, don’t think to add the English word ‘achoo’ to this most natural of actions” (Emma Tracey, bbc.com).  “To me, deaf sneezes sound more like this: a heavy breath is taken, then a sharper, faster sound of air being released as the sneeze occurs.  There is none of this ‘aahhh’ sound added as they breathe in.  And none of that ‘choo’ malarkey as said sneeze is released.” (Charlie Swinbourne, The Question: Do Hearing People Fake Their Sneezes? We Need to Know, limpingchicken.com).

People want to conform to the norm.  They are influenced by those around them.  Charlie Swinbourne suggests, “As they sense a sneeze coming, the hearing person’s brain sends out an alert saying: ‘Emergency! You are about to sneeze in public.  Make this sound normal” (Charlie Swinbourne, limpingchicken.com).

I don’t really care about the sound of your sneezes.  However, I do care about spiritual influence.  Who is influencing us?  “He who walks with wise men will be wise, but the companion of fools will be destroyed” (Proverbs 13:20).  “As iron sharpens iron, so a man sharpens the countenance of his friend” (Proverbs 27:17).  The ESV Study Bible comments, “Since the word ‘face’ (Hb. Panim) can refer to the edge of an axe or sword (Eccl. 10:10; possibly Ezek. 21:16), the image is that the interaction with a good man (both as he encourages and corrects) hones one’s skill in handling challenges.”  “Do not be deceived: Evil company corrupts good habits” (1 Corinthians 15:33). 

How much time are we spending with the best of all examples, Jesus?  Spending time with Jesus changed Peter and John.  “Now when they saw the boldness of Peter and John, and perceived that they were uneducated and untrained men, they marveled.  And they realized that they had been with Jesus” (Acts 4:13).  It will change us as well.  “We all, beholding as in a mirror the glory of the Lord, are being transformed into the same image from glory to glory” (2 Corinthians 3:18). Robert H. Mounce comments, “Taking the participle (beholding- B.H.) in the instrumental sense we read, ‘We all are being changed into the image of Christ by beholding the glory of the Lord.’  Transformation into the likeness of Christ is the inevitable result of gazing upon his glory.  We become like that which dominates our thoughts and affections.  Like Nathaniel Hawthorne’s ‘great stone face,’ which shaped the life of the one who spent his days looking at the craggy representation of all that was held to be good and pure, so also does the believer gradually take on the family resemblance to his or her Lord as they spend their time contemplating the glory of God.  Notice that the participle is present tense.  It is a continual contemplation that effects the transformation.  As the participle is present tense, so also is the finite verb ‘are being changed.’  The transformation keeps pace with the contemplation.  They are inextricably bound together.  By continuing to behold the glory of the Lord we are continually being transformed into his image” (William D. Mounce, Basic of Biblical Greek Grammar, p. 298).  There is no other way.  Let us be ever “looking unto Jesus” (Hebrews 12:2).  “Grow in the grace and knowledge of our Lord and Savior Jesus Christ” (2 Peter 3:18).  He left us an example that we should follow in His steps (1 Peter 2:21 cf. John 13:34; Philippians 2:5; Hebrews 12:1-4; 1 John 3:16-18).