Check out my program

#include <stdio.h>
#include <unistd.h>
#define LEN 15
int print(i,j) {
for (; i < LEN; ++i)
printf(" ");
puts("a");
usleep(50000);
return 0;
}
int main(void)
{
int i, j;
for(;;) {
for (j = 0; j < LEN; print(i), ++j)
i = j;
for (j = 0; j < LEN; print(i), ++j)
i = LEN-1-j;
}
return 0;
}

Do you like it?

At first I tried to make it be the SICP snake, with the head going down, but it was too hard for me.

//Cee
#include <stdio.h>
#include <unistd.h>
#define LEN 15
print(i,j,z ,a2 ,a3 ,a5 ,a7 ,a11 ,a13 ,a17 ,a19 ,a23 ,a29 ,a31 ,a37 ,a41){
while (i++ < LEN)putchar(' ');
puts("x""y""z"); usleep(20000);}
main(i,j){
for (j = 0; j++ < LEN; print(i=j));
for (j = 0; j++ < LEN; print(i=LEN-j));
main(i,j);}