threshold in a first flow direction and not oscillate the flow of the fluid above the oscillation threshold in a second flow direction. [0027] Clause 23: In one example, a method comprises: introducing a catheter into vasculature of a patient, the catheter coupled to a fluid flow sensor comprising: a fluid inlet configured to receive fluid from a catheter; a fluid outlet configured to discharge the fluid; and a flow oscillator configured to oscillate flow of the fluid through the fluid flow sensor to generate flow-induced vibrations; and after introducing the catheter into the vasculature of the patient, aspirating a fluid through the catheter. [0028] Clause 24: In some examples of the method of clause 23, the method further comprises during the aspirating, generating, by the flow oscillator, the flow-induced vibrations in response to flow of the fluid through the flow oscillator from catheter. [0029] Clause 25: In some examples of the method of clause 24, the method further comprises during the aspirating and in response to an increase in at least one of a magnitude or frequency of the flow-induced vibrations, repositioning the catheter in the vasculature of the patient. [0030] The examples described herein may be combined in any permutation or combination. [0031] The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description and drawings, and from the claims. [0032] FIG. 1 is a schematic diagram illustrating an example aspiration system that includes a fluid flow sensor configured to generate flow-induced vibrations in response to receiving fluid flow from a catheter. [0033] FIG. 2A is conceptual block diagram illustrating the aspiration system of FIG. 1 at an infusion state. [0034] FIG. 2B is a conceptual block diagram illustrating the aspiration system of FIG. 1 at an unblocked aspiration state. [0035] FIG. 2C is a conceptual block diagram illustrating the aspiration system of FIG. 1 at a blocked aspiration state. [0036] FIG. 3A is a diagram of a fluid flow sensor that includes a fluid oscillator having a fluid diverting portion. BRIEF DESCRIPTION OF THE DRAWINGS