I want to experiment with the new Pd feature of the
[snake_in~]/[snake_out~] objects, specifically with [snake_in~]. In Pd's
source files (in d_misc.c) I read the following in [snake_in~]'s dsp
routine:
```
static void snake_in_tilde_dsp(t_snake_in *x, t_signal **sp)
{
   int i;
       /* create an n-channel output signal. sp has n+1 elements. */
   signal_setmultiout(&sp[x->x_nchans], x->x_nchans);
       /* add n copy operations to the DSP chain, one from each input */
   for (i = 0; i < x->x_nchans; i++)
        dsp_add_copy(sp[i]->s_vec,
           sp[x->x_nchans]->s_vec + i * sp[0]->s_length, sp[0]->s_length);
}
```
There is no perform routine, so my question is, how do I deal with snake
signals in a perform routine? How do I unpack them? Where is this
happening in Pd's source code, so I can have a look?