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.

//even better
#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 ,a43 ,a47 ,a53 ,a59 ,a61 ,a67 ,a71 ,a73 ,a79 ,a83 ,a89 ,a97 ,a101 ,a103 ,a107 ,a109 ,a113 ,a127 ,a131 ,a137 ,a139 ,a149 ,a151 ,a157 ,a163 ,a167 ,a173 ,a179 ,a181 ,a191 ,a193 ,a197 ,a199 ,a211 ,a223 ,a227 ,a229 ,a233 ,a239 ,a241 ,a251 ,a257 ,a263 ,a269 ,a271 ,a277 ,a281 ,a283 ,a293 ,a307 ,a311 ,a313 ,a317 ,a331 ,a337 ,a347 ,a349 ,a353 ,a359 ,a367 ,a373 ,a379 ,a383 ,a389 ,a397 ,a401 ,a409 ,a419 ,a421 ,a431 ,a433 ,a439 ,a443 ,a449 ,a457 ,a461 ,a463 ,a467 ,a479 ,a487 ,a491 ,a499 ,a503 ,a509 ,a521 ,a523 ,a541 ,a){
for (; i++ < LEN; )
putchar(' ');
puts("OOOOO");
usleep(20000);

}
main(){ st:;
int i,j;
for ( j = 0; j++ < LEN; print(i=j));
for (j = 0; j++ < LEN; print(i=LEN-1-j));
goto st;}