C (gcc) with -m32, 90 85 83 bytes

• -2 thanks to ceilingcat

c,v;f(char*s){for(v=s;v**s;)index("aeiou",c=*s++)&&printf("shm",v=0);puts(v?:--s);} 

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C (gcc) with -m32, 90 85 83 79 bytes

• -2 thanks to ceilingcat
• -4 by removing an unused variable

v;f(char*s){for(v=s;v**s;)index("aeiou",*s++)&&printf("shm",v=0);puts(v?:--s);} 

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C (gcc) with -m32, 90 85 bytes

c,v;f(char*s){for(v=s;v&&(c=*s++);)index("aeiou",c)&&printf("shm",v=0);puts(v?:--s);} 

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C (gcc) with -m32, 90 85 83 bytes

• -2 thanks to ceilingcat

c,v;f(char*s){for(v=s;v**s;)index("aeiou",c=*s++)&&printf("shm",v=0);puts(v?:--s);} 

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C (gcc) with -m32, 90 bytes

m,c,v;f(char*s){for(m=v=s;m&&(c=*s++);)index("aeiou",c)&&printf("shm",m=0);puts(m?v:--s);} 

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C (gcc) with -m32, 90 85 bytes

c,v;f(char*s){for(v=s;v&&(c=*s++);)index("aeiou",c)&&printf("shm",v=0);puts(v?:--s);} 

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