If they had more time, Theseus would've replied to Newt's comment, saying something like 'now I can't very well have that happen,' but the older Scamander has seemingly switched gears-- his mind entirely focused on the mission now. Even without his normal magic and power, it's obvious that he's doing his best to look the Head Auror that he's known to be: focused and ready for any attack.

Theseus can already feel the vibrations becoming more intense by the moment, so he steps a few feet back, away from Newt, while keeping the noise stationary as a focus point for the moles. He still has his wand raised to keep the sound going, but the Auror doesn't want to be standing right there when the moles pop up.

And it's probably just in time too, for three of the moles suddenly burst up from the ground, swinging wildly at the open air that still's ringing from the sound. It's truly fortunate that they're unable to see, as two of them are still in a frenzy, but one's able to sense the feint noise coming from Theseus' wand, and whips one of its infected strings at the wizard. Theseus manages to block the attack in time, throwing up a protective charm, but it's likely that he won't be able to do anything else but defend himself right now.

Especially as the other two moles have finally turned their attention on him as well, hearing the sound of the shield blocking an attack.