A related joke:
Why is a FIL called shver and the SIL called eidim?
At the tenaim the FIL promises x years of support. After the wedding he reneges and the SIL takes him to bet din. The FIL says he never promised anything so bet din tells the SIL “SHVER” (swear a shvuas hessiss so you can take the money). The son-in-law answers “I don’t have to. I have EIDIM that he promised me!”