Facial nerve palsy at sternomastoid canal can cause-
Below stylomastoid foramen, facial nerve gives following branches: - Posterior auricular branch, muscular branches (stylohyoid & posterior belly of digastric) and terminal (peripheral) branches.
Lesion at sternomastoid foramen : -

i)    Will spare

Greater superficial petrosal nerve → Lacrimation present.
Nerve to stapedius → Normal stapedial reflex and no hyperacusis.
Chorda tympani → Normal salivation and a taste sensation in anterior 2/3 of the tongue.

ii) Will involve

Terminal (peripheral) branches → Paralysis of muscles of facial expression. Corneal reflex will also be lost because efferent fibres of corneal reflex are derived from peripheral branches of the facial nerve.
Loss of corneal reflex at side of lesion
Loss of taste sensation anterior 2/3 of ipsilateral tongue
Loss of lacrimation at side of lesion
Hyperacusis