Passage 10.17.13
πλὴν δὲ ἢ βοτάνης μιᾶς καθαρεύει καὶ ἀπὸ φαρμάκων ἡ νῆσος ὅσα ἐργάζεται θάνατον· ἡ πόα δὲ ἡ ὀλέθριος σελίνῳ μέν ἐστιν ἐμφερής, τοῖς φαγοῦσι δὲ γελῶσιν ἐπιγίνεσθαι τὴν τελευτὴν λέγουσιν. ἐπὶ τούτῳ δὲ Ὅμηρός τε καὶ οἱ ἔπειτα ἄνθρωποι τὸν ἐπὶ οὐδενὶ ὑγιεῖ Σαρδάνιον γέλωτα ὀνομάζουσι. φύεται δὲ μάλιστα ἡ πόα περὶ τὰς πηγάς, οὐ μέντοι μεταδίδωσί γε καὶ τῷ ὕδατι τοῦ ἰοῦ. τὸν μὲν δὴ περὶ τῆς Σαρδοῦς λόγον ἐπεισηγαγόμεθα ἐς τὴν Φωκίδα συγγραφήν, ὅτι οὐχ ἥκιστα καὶ ἐς ταύτην οἱ Ἕλληνες τὴν νῆσον ἀνηκόως εἶχον·
Except for a single herb, the island is free of plants and poisons that cause death. The deadly herb resembles celery, and they say that those who eat it die while overcome by laughter. For this reason, Homer and later people have named any unnatural laughter "Sardonic." The herb grows especially around springs, but it does not pass its poison into the water. I have included this account concerning Sardinia in my description of Phocis because among the Greeks, not least among the Phocians, ignorance of this island was widespread.