If the beis din and all of Israel saw [the moon], or if the witnesses were interrogated, but they did not manage to say, “It is sanctified,” before it grew dark —- it is full.  If only beis din saw it, two [of them] should stand and testify before the others, and they should say, “It is sanctified, it is sanctified!”  If three saw it and they constitute a beis din, [then] two should stand up and set some of their colleagues beside the single one and testify before them, and say, “It is sanctified, it is sanctified!” For an individual is not trusted alone.

All shofars are valid except for that of a cow, because it is [called] a keren.  R’ Yose said: But are not all shofars called keren, as it is said: When they make a long blast with the ram’s keren?