"Rats!" is a popular insult hurled a politicians thought to be corrupt in Colombia.
But rather than shouting the word from the visitors' gallery as protesters have before, an unidentified person threw live rodents onto conservative senators on Tuesday.
The reaction to the rodents was varied.
Some senators shrieked and laughed and took their mobiles out to film the animals while others stormed the gallery to find their owner.
Senators including the Green Party's Angélica Lozano attempted to take footage of the animal hiding behind a monitor. Senators can be heard trying to identify the animal with one insisting that its tail is typical of a hamster.
La puerta de las barras están cerradas. La plenaria suspendida, mientras revisan las cámaras de seguridad para identificar quien arrojó la bolsa plástica negra.
Mucha demora para revisar la cámara de seguridad pic.twitter.com/vuQ83Zor1G
— Angélica Lozano Correa (@AngelicaLozanoC) December 11, 2018
End of Twitter post by @AngelicaLozanoC
Ms Lozano had been co-presiding the plenary session when the incident happened. She calmly condemned the throwing of the animals saying: "We respect freedom of expression, but you can't throw animals. It shows a lack of respect."
The rodents were released as senators were about to discuss whether to strip a magistrate accused of corruption of his judicial immunity.
Senator Santiago Valencia told Colombian media that four white mice were thrown from the gallery inside a plastic bag full of confetti "which acted like a sort of parachute".
Mr Valencia said that he managed to grab the bag and close it while three of the rodents were still inside but that one had already escaped.
Witnesses said the target of the protest was former President Álvaro Uribe and his colleagues from the conservative Democratic Centre party.
Mr Uribe climbed the stairs to the visitors' gallery to investigate while other senators milled about and one took the opportunity to finish his sandwich.
The person who threw the bag has not yet been identified.