Letters that make up to their necks
s, o, e, k, n, p, c, h, r, t, i, u are letters that make 'up to their necks'
Words within up to their necks
neck, he, IR, EC, heir, He, Eck, up to, up, KS, NE, NEC, Ir, Ne, Th are words within 'up to their necks'