verb/tə.ni.ʁ‿ɑ̃.n‿a.lɛn/
to keep someone on their toes; to keep someone in bated breath, to keep someone in a state of uncertainty, be it hopeful or fearful
“[Une pyromane a] tenu les policiers et pompiers en haleine en fin de soirée... en mettant le feu à plusieurs poubelles.” — A pyromaniac kept police and firefighters on their toes last night... by setting fire to several trash cans.