So I'm reading this manga, and at one point person A brings out a syringe and starts explaining to person B about how she needs to recieve what's in the syringe for a procedure to work, and then goes on to start explaining why which is when person B interupts them to say:
えいつ or maybe えいっ
Which is followed by:
Person A: ええ！？> Eeeh?
Person B: どうかしました？ > Is something wrong?
Person A: あはは！ いぇ…あまりにためらいがなかったもので > Ahaha! No...it’s the lack of any hesitation.
I've hit the dictionaries and there isn't anything for えいつ and while there are some entries for えい none of them seem anything relvant.
Given the context to me it seems like B said some equivalent of "Okay", which surprises A who expected to need to talk B into it.
Basically, is this a typo and in either case what's the meaning?