Two words I'm surprised to find are not cognates: quail (n.) and quail (v.).
I'd always assumed the verb was derived from the noun (i.e. "acting in a way similar to a small skittish game bird") but they're from entirely distinct sources. The noun is an onomatopoeia coloured by the PIE root for "quail" and thus related to German Wachtel, Ancient Greek ὄρτυξ, etc. The verb, on the other hand, is from PGmc *kwelaną "suffer" and, thus, is cognate to German quälen "torture", Swedish kvälja "arraign", etc.
"Richmond is a real scholar; Owen just learns languages because he can't bear not to know what other people are saying."--Margaret Lattimore on her two sons