characteristics. Example characteristics may include, but are not limited to, amplitude of vibrations, frequency of vibrations, and the like. In some examples, fluid oscillator 20 is configured to generate vibrations having a frequency between about 15 hertz and about 30 hertz at a flow rate of the fluid between about 3 milliliters per second and about 5 milliliters per second. [0066] In some examples, fluid oscillator 20 may be configured to increase a magnitude of the vibrations in response to an increase in a flow rate of the fluid through fluid oscillator 20. For example, fluid oscillator 20 may include a moveable oscillating portion configured to impact one or more structures within fluid oscillator 20 with a greater amount of force as a flow rate of fluid through fluid oscillator 20 increases. In some examples, fluid oscillator 20 may be configured to increase a frequency of the vibrations in response to an increase in a flow rate of the fluid through fluid oscillator 20. For example, fluid oscillator 20 may include a flow diverting portion configured to oscillate flow between two or more states at a rate that is proportional to a flow rate of fluid through fluid oscillator 20. In this way, a clinician operating aspiration system 10 may receive an indication of both a presence of fluid flow, indicated by a presence of vibrations, and a change in a degree of fluid flow, indicated by either a change in magnitude of the vibrations or a change in frequency of the vibrations. [0067] In some examples, fluid oscillator 20 may be configured to change at least one of an amplitude of the vibrations or a frequency of the vibrations in response to a change in density of the fluid flowing through fluid oscillator 20. For example, saline has a density of about 2.16 g/cm$^{3}$, while blood has a density of about 1.08 g/cm$^{3}$. As a composition of the fluid removed from catheter 12 changes, such as when a thrombus is engaged by catheter 12, a density of the fluid may change, which may affect flow rate, turbulence, or other flow characteristics that may affect an amplitude or frequency of the vibrations. For example, a change in amplitude and/or frequency of the vibrations may occur when the composition of the fluid removed from catheter 12 changes from undiluted blood (or substantially undiluted blood) to a mixture of saline and blood, to undiluted saline (or substantially undiluted saline), or from one to another of any of the foregoing. This change in the vibrations can provide useful information to the operator, including confirmation that the aspiration of vessel contents (blood and/or thrombus) has commenced, and that any saline left in the catheter 12 (e.g. from priming or flushing) has been removed. This may in turn function as a notice to the operator that the some or all